Vibratory gyroscope

ABSTRACT

A vibratory gyroscope including an elongated vibrator having a central (neutral) axis (Y-axis), a drive unit for deforming the first direction such that the vibrator vibrates in a first (X) direction, an added mass attached to the vibrator at a position offset from the central axis in a second (Z) direction, and a detector formed on the vibrator. Rotation of the vibratory gyroscope about the second (Z) direction during vibration in the second direction causes Coriolis force to acting on the added mass in a direction parallel to the central axis. Because the added mass is offset from the central axis, a resulting vibration in the second (Z) direction is produced, which is detected by the detector. With this arrangement, the central axis of the vibrator is placed in parallel with the surface of rotation of the rotating system. Thus, rotations about two or three axes in each direction can be detected in such a manner that noise generation is prevented.

This application is a continuation of Ser. No. 08/594,616 filed on Oct.27, 1995, now U.S. Pat. No. 5,708,320.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to gyroscopes for detecting the rotationalangular velocity of an object, and in particular to vibratory gyroscopeswhich determine the rotational angular velocity by determining theCoriolis force acting on the object.

2. Description of the Related Art

Gyroscopes are used for detecting rotational angular velocity in carnavigation systems, inertial navigation systems and attitude controlsystems for aircrafts and ships, attitude control systems for robots andunmanned vehicles and apparatuses for producing a stable image in TVcameras and video cameras.

The gyroscopes used in the foregoing various industrial applicationsmust be small in size. Therefore, vibratory gyroscopes, which aretypically smaller than other types of gyroscopes, have attractedattention.

FIG. 32 shows a conventional vibratory gyroscope. The vibratorygyroscope comprises a columnar vibrator 1 made of isoelastic metal(Elinvar) to which a drive piezoelectric device 2 and a detectionpiezoelectric device 3 are secured. When the vibrator 1 is rotated abouta Z-axis while the drive piezoelectric device 2 supplies, to thevibrator 1, bending vibrations in the direction of an X-axis, Coriolisforce acts on the vibrator 1 such that the vibrator 1 is vibrationallydeformed in the Y-axis direction. The amount of deformation in theY-axis direction is detected by the piezoelectric device 3 as a voltagesignal.

Assuming that the mass of the vibrator 1 is m, the velocity of theapplied vibrations in the X-axis direction is v (a vector value) and theangular velocity about the Z-axis is ω, the Coriolis force F (a vectorvalue) is as follows:

    F=2m(v×ω)

where symbol x indicates a vector cross product.

As described above, the Coriolis force F is proportional to the angularvelocity ω. Therefore, if the deforming vibrations of the vibrator 1 inthe Y-axis direction are converted into a voltage signal by thedetection piezoelectric device 3, the angular velocity ω can be obtainedby measuring the voltage signal.

However, because the vibratory gyroscope shown in FIG. 32 has astructure in which the vibrator 1 is driven to vibrate in the X-axisdirection and is deformed in the Y-axis direction by the Coriolis force,only an angular velocity ω about the Z-axis (that is, the longitudinalor major axis of the vibrator 1) can be detected. Therefore, thevibratory gyroscope can only be mounted on a surface of a rotatingobject which is perpendicular to the Z-axis. This restricts the use ofthe vibratory gyroscope in a variety of apparatuses in which such asurface is not readily available.

Moreover, if it is desired to detect rotational angular velocity in two-or three-dimensional directions using the vibratory gyroscope of theforegoing type, two or more vibrators 1 of the type shown in FIG. 32must be arranged such that the major axes of the respective vibrators 1are perpendicular to each other. Further, when it is desired to detectrotational angular velocity in three-dimensional directions, two of thevibratory gyroscopes may be arranged in the plane of a substrate, but itis necessary to arrange the third vibratory gyroscope such that itprojects perpendicular to the substrate. In this arrangement, a spacerequired for the three vibratory gyroscopes is substantially increasedto accommodate the third vibratory gyroscope.

Furthermore, the vibratory gyroscope shown in FIG. 32 is only able todetect bending vibrations due to the Coriolis force--that is, thevibratory gyroscope cannot detect torsional vibrations. Since thevibration mode is limited only to bending vibrations, the applicationsof the conventional vibratory gyroscope is narrowed undesirably.

In addition, the above-mentioned conventional vibratory gyroscope isonly able to detect the angular velocity of a rotating system about oneaxis. In order to detect the angular velocity of rotating system abouttwo axes, two conventional vibrators must be employed. In order todetect angular velocity of a rotating system about three axes, threeconventional vibrators must be employed.

SUMMARY OF THE INVENTION

In order to overcome the foregoing problems, an object of the presentinvention is to provide a vibratory gyroscope in which Coriolis forceacting in a first direction produces deformation of a vibrator in asecond direction perpendicular to the first direction so that a majoraxis of the vibrator is disposed in parallel to the rotational surfaceof the rotating system (i.e., perpendicular to the axis of rotation),thereby allowing the vibrator to be freely mounted the on the rotationalsurface.

Another object of the present invention is to provide a vibratorygyroscope that uses an added mass so as to detect the angular velocityof a rotating system about an axis other than the major axis of thevibrator and as well as to eliminate an influence of noise on therotating system.

Another object of the present invention is to stably drive the vibratorygyroscope and stably detect rotations by providing a plurality ofvibrators and by vibrating and deforming each vibrator in symmetricaldirections.

Another object of the present invention is to detect rotations in eachdirection about two or three axes using a single vibratory gyroscope.

According to one aspect of the present invention, there is provided avibratory gyroscope including a vibrator having a central (neutral)axis, first piezoelectric elements (drive means) mounted on the vibratorfor deforming and vibrating the vibrator in a first direction, an addedmass for causing Coriolis force acting on the vibrator in a seconddirection (perpendicular to the first direction) when the vibrator isplaced in a rotating system to act on a position deviated from thecentral axis of the vibrator to deform and vibrate the vibrator, andsecond piezoelectric elements (detection means) for detectingdeformation and vibrations of the vibrator.

According to another aspect of the present invention, there is provideda vibratory gyroscope including a plate-like vibrator having a centralaxis, drive means for deforming and vibrating the vibrator in a firstdirection along the surface of the plate, an added mass for causingCoriolis force acting in a direction perpendicular to the firstdirection in the surface of the vibrator when the vibrator is placed ina rotating system about an axis perpendicular to the surface of thevibrator to act on a position deviated from the central axis of thevibrator to deform and vibrate the vibrator, and detection means fordetecting deformation and vibrations of the vibrator.

In the foregoing embodiment, one or more grooves are cut into a flatmember, thereby separating the flat member into a plurality of parallelvibrators separated by the grooves. Added masses are provided for eachof the plurality of the vibrators and the drive means of each of thevibrators are controlled to bendingly-vibrate in opposite phases.

According to another aspect of the present invention, there is provideda vibratory gyroscope including a vibrator having a central axis, drivemeans for contracting, expanding and deforming the vibrator in adirection of the central axis of the vibrator, an added mass for causingCoriolis force acting on the vibrator in a direction perpendicular tothe first direction when the vibrator is placed in a rotating systemabout an axis perpendicular to the central axis to act on a positiondeviated from the central axis of the vibrator to torsionally deform thevibrator, and detection means for detecting torsional vibrations of thevibrator.

In each of the foregoing aspects, the added mass can be formed bysecuring, to a leading portion or the like of the vibrator, anindividual mass (a weight) at a position deviated from the central axis(an axis passing through the center of gravity of the cross section ofthe vibrator, that is, a neutral axis of the vibrator). The added massmay be formed by forming a cutting portion or a groove in the leadingportion or the like of the vibrator to change the distribution of massesin the direction of the cross section with respect to the central axis.The added mass can also be formed by bending the leading portion of thevibrator.

According to the present invention, the vibrator is deformed andvibrated using piezoelectric devices, and piezoelectric devices are alsoused to detect vibrational components of the vibrator caused by theCoriolis force. The vibrator may be formed by applying a piezoelectricdevice serving as a portion of the drive means or a piezoelectric deviceserving as a portion of the detection means to isoelastic metal such asElinvar. The vibrator may be formed by stacking piezoelectric material(piezoelectric ceramic) on a plate-like member made of isoelastic metalsuch as Elinvar and by applying or stacking a drive electrode serving asa portion of the drive means or a detection electrode serving as aportion of the detection means on the piezoelectric material. In theexamples below, the vibrator is made of a piezoelectric material, suchas piezoelectric ceramic or crystal, the crystal orientation of which isrealized by a Z-crystal plate at a cut angle rotated +2° about theX-axis. Furthermore a drive electrode serving as a portion of the drivemeans and a drive electrode serving as a portion of the detection meansare applied or stacked on the surface of the piezoelectric material. Thedrive means according to the present invention includes a driveelectrode provided for the piezoelectric material and a drive powersource for supplying high-frequency electric power. The detection meansincludes a detection electrode provided for the piezoelectric materialand a detection output terminal. In the case where the differentdetection voltages (or electric currents) are compensated, adifferential circuit, a subtraction circuit or a phase differencecircuit is, as a compensation means, provided for the detection means.Furthermore, an addition means for adding detection outputs in the samephase may be provided.

In the following description, the first direction is the same directionas the drive direction in which the vibrator is vibrated, whereas thesecond direction is a direction perpendicular to the first direction.The second direction is the direction of the axis of rotation of thevibratory gyroscope. The third direction is a direction perpendicular toeach of the first direction and the second direction, the thirddirection being the direction of the major (central) axis of thevibrator.

According to another aspect of the present invention, there is provideda vibratory gyroscope including: a vibrator having a central axisaligned in the third direction, drive means for deforming and vibratingthe vibrator in the first direction, an added mass for causing Coriolisforce acting on the vibrator when the vibrator is placed in a rotatingsystem to act on a position deviated from the central axis of thevibrator to deform and vibrate the vibrator in the first direction, anddetection means for detecting deformation and vibrations of the vibratorin the first direction.

The foregoing vibratory gyroscope is arranged such that the vibrator isvibrated in the first direction due to the Coriolis force in therotating system and the vibration component is detected. When thevibratory gyroscope is given the rotations of the vibrator about themajor axis, vibrations in the second direction are generated in thevibrator as well as the foregoing vibrations in the first direction.Therefore, the piezoelectric device or the detection electrode of thedetection means is disposed at a position at which it is capable ofdetecting only the component in the first direction so thatsuperimposing of the vibration component in the second direction on thedesired detection output is prevented.

In the case where the piezoelectric device or the detection electrodedetects vibrations in the second direction, the detection means may haveelectrodes so disposed as to be capable of detecting a vibrationcomponent in the first direction and compensating a detection output dueto a vibration component in the second direction, or a differentialmeans (a differential circuit) may be disposed.

Furthermore, detection means for detecting a vibration componentgenerated in the vibrator in a second direction perpendicular to thefirst direction due to Coriolis force given in a rotating system about amajor axis of the vibrator may be provided in addition to the detectionmeans for detecting the vibration component in the first direction sothat the two detection means respectively detect rotations about twoaxes.

In each aspect of the present invention, the vibratory gyroscope can beformed by disposing one flat or columnar vibrator. If two or morevibrators are disposed in parallel and as well as the vibrators areseparated from each other by grooves formed in an elastic member so asto cause each vibrator to be vibrated in a symmetrical mode in which theamplitudes are in the opposite directions, vibrations of each vibratorcan be stabilized.

In the foregoing case, the vibratory gyroscope includes a plurality ofvibrators, drive means for deforming and vibrating the plurality of thevibrators in opposite amplitude directions in a first direction, addedmasses for causing Coriolis force acting on each of the vibrators whenthe vibrators are placed in a rotating system to act on a positiondeviated from the central axis of the vibrators to deform and vibratethe vibrators in opposite amplitude directions in the first direction,and detection means for detecting deformation and vibrations of at leastone vibrator in the first direction.

In the foregoing case, it is preferable that three vibrators areprovided, right and left vibrators and a central vibrator are deformedand vibrated by the drive means in opposite amplitude directions in afirst direction (X), in which the vibrators are arranged, and the rightand left vibrators are deformed and vibrated in opposite amplitudedirections in the first direction (X) due to the added mass whenCoriolis force acts on the right and left vibrators.

It is also preferable that three vibrators are provided, right and leftvibrators and a central vibrator are deformed and vibrated by the drivemeans in opposite amplitude directions in the first direction (Z), inwhich the vibrators are arranged, and the right and left vibrators aredeformed and vibrated in opposite amplitude directions in the firstdirection (Z) due to the added mass when Coriolis force acts on theright and left vibrators.

Also in the case where a plurality of vibrators are provided, thedetection means may have electrodes so disposed as to detect a vibrationcomponent in the first direction and compensating a detection output dueto a vibration component in a second direction when each of the vibratoris vibrated in the second direction perpendicular to the first directiondue to Coriolis force applied to system rotating about a major axis (Y)of the vibrator.

A detection means for detecting a vibration component generated in thevibrator in a second direction perpendicular to the first direction dueto Coriolis force given in a rotating system about a major axis (Y) ofthe vibrator is provided in addition to the detection means fordetecting the vibration component in the first direction, and the twodetection means enable rotations about two axes to be detectedindividually.

An example of the structure capable of detecting rotations about the twoaxes has a structure such that three vibrators are provided, right andleft vibrators and a central vibrator are deformed and vibrated by thedrive means in opposite amplitude directions in the first direction, theright and left vibrators are deformed and vibrated in opposite amplitudedirections in the first direction due to the added mass when Coriolisforce acts on the right and left vibrators, and the right and leftvibrators and the central vibrator are deformed and vibrated in oppositeamplitude directions in the second direction perpendicular to the firstdirection when Coriolis force is given from a rotating system about amajor axis.

According to the present invention, one vibratory gyroscope is able todetect rotations about each of three axes that are perpendicular to oneanother.

An example of the foregoing structure includes a plurality of vibratorsof a first set and a plurality of vibrators of a second set which aredeformed and vibrated due to a piezoelectric effect and which extend inopposite directions, drive means for deforming and vibrating theplurality of the vibrator of the first set in opposite amplitudedirections in the first direction (X), added masses for causing Coriolisforce acting on the vibrators of the first set when the vibrators areplaced in a rotating system to act on a position deviated from thecentral axis of each of the vibrators to deform and vibrate thevibrators of the first set in opposite amplitude directions in the firstdirection (X), detection means for detecting deformation and vibrationsof the vibrators of the first set in the first direction (X), detectionmeans for detecting a vibration component given to the vibrators of thefirst set in a second direction (Z) perpendicular to the first directiondue to Coriolis force given in a rotating system about a different axis(Y), drive means for deforming and vibrating the plurality of thevibrators of the second set in opposite amplitude directions in thesecond direction (Z) perpendicular to the first direction, added massesfor causing Coriolis force acting on the vibrators of the second setwhen the vibrators are placed in a rotating system to act on a positiondeviated from the central axis of each of the vibrators to deform andvibrate the vibrators of the second set in opposite amplitude directionsin the second direction (Z), and detection means for detectingdeformation and vibrations of the vibrators of the second set in thesecond direction (Z) so that rotations about three axes are detectedindividually.

Other and further objects, features and advantages of the invention willbe evident from the following detailed description of the preferredembodiments in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a vibratory gyroscope according toa first example of the present invention;

FIG. 2A is a side view showing a state where the vibratory gyroscopeaccording to the first example is bending-vibrated in a primaryresonance mode;

FIG. 2B is a view of explanatory showing a state where the vibratorygyroscope is bending-vibrated in a secondary resonance mode;

FIG. 3 is an enlarged cross sectional view taken along line III--III ofFIG. 1 and showing the structure of the piezoelectric device providedfor the vibrator;

FIG. 4 is a perspective view showing a vibratory gyroscope according toa modification of the first example;

FIG. 5 is a perspective view showing a bending-vibration mode of thevibrator shown in FIG. 4;

FIG. 6 is a perspective view showing a vibratory gyroscope according toanother modification of the first example;

FIG. 7 is a perspective view showing a bending-vibration mode of thevibrator shown in FIG. 6;

FIG. 8 is a perspective view showing a vibratory gyroscope according toa second example of the present invention;

FIG. 9A is a plan view showing the vibratory gyroscope shown in FIG. 8;

FIG. 9B is a side view showing the foregoing vibratory gyroscope;

FIGS. 10A and 10B are diagrams showing a modification of the secondexample, in which FIG. 10A is a plan view of the vibratory gyroscope,and FIG. 10B is a side view of the same;

FIG. 11 is a perspective view showing a vibratory gyroscope according toa third example of the present invention;

FIG. 12 is a perspective view showing a vibratory gyroscope according toa modification of the third example;

FIG. 13 is a perspective view showing a vibratory gyroscope according toa fourth example of the present invention;

FIG. 14 is a view of explanatory showing a vibration mode of thevibrator according to the fourth example;

FIG. 15 is a cross sectional view taken along line XV--XV of FIG. 13 andshowing the directions of electric fields of crystal forming thevibrator according to the fourth example and the configuration ofelectrodes of the same;

FIG. 16 is a perspective view showing a vibratory gyroscope according toa fifth example of the present invention;

FIGS. 17A and 17B are diagrams showing the vibration mode of thevibrator according to the fifth example, in which FIG. 17A shows thedrive vibration mode and FIG. 17B shows the detection vibration mode;

FIG. 18A is a diagram showing the polarizing directions of thepiezoelectric material forming the vibrator according to the fifthexample and the configuration of the electrodes of the same, FIG. 18Abeing a cross sectional view taken along line XVIII--XVIII of FIG. 16;

FIG. 18B is a diagram showing the directions of electric fields and theconfiguration of the electrodes in the case where the vibrator is madeof crystal, FIG. 18B being a cross sectional view taken along lineXVIII--XVIII of FIG. 16;

FIG. 19 is a perspective view showing a vibratory gyroscope according toa sixth example of the present invention;

FIGS. 20A and 20B are diagrams showing vibration modes of the vibratoraccording to a sixth example, in which FIG. 20A shows a drive vibrationmode and FIG. 20B shows a detection vibration mode;

FIG. 21A is a diagram showing the polarizing directions of thepiezoelectric material forming the vibrator according to the sixthexample and the configuration of the electrodes of the same, FIG. 21Abeing a cross sectional view taken along line XXI--XXI of FIG. 19;

FIG. 21B is a diagram showing the directions of electric fields and theconfiguration of the electrodes in the case where the vibrator is madeof crystal, FIG. 21B being a cross sectional view taken along lineXXI--XXI of FIG. 19;

FIG. 22 is a perspective view showing a vibratory gyroscope according toa seventh example of the present invention;

FIGS. 23A and 23B are diagrams showing vibration modes of the vibratoraccording to the seventh example, in which FIG. 23A shows the drivevibration mode, and FIG. 23B shows the detection vibration mode;

FIG. 24A is a diagram showing the polarizing directions and theconfiguration of the electrodes of the vibrator according to the seventhexample, FIG. 24A being a cross sectional view taken along lineXXIV--XXIV of FIG. 22;

FIG. 24B is a diagram showing the directions of electric fields and theconfiguration of the electrodes in the case where the vibrator is madeof crystal, FIG. 24B being a cross sectional view taken along lineXXIV--XXIV of FIG. 22;

FIG. 25 is a perspective view showing a vibratory gyroscope according toan eighth example of the present invention;

FIGS. 26A, 26B and 26C are diagrams showing vibration modes of thevibrator according to the eighth example, in which FIG. 26A shows thedrive vibration mode, FIG. 26B shows the detection vibration mode of therotations about the Z-axis, and FIG. 26C shows the detection vibrationmode of the rotations about the Y-axis;

FIG. 27A is a diagram showing the polarizing directions of thepiezoelectric material forming the vibrator according to the eighthexample and the configuration of the electrodes of the same, FIG. 27Abeing a cross sectional view taken along line XXVII--XXVII of FIG. 25;

FIG. 27B is a diagram showing the directions of electric fields and theconfiguration of the electrodes in the case where the vibrator is madeof crystal, FIG. 27B being a cross sectional view taken along lineXXVII--XXVII of FIG. 25;

FIG. 28 is a perspective view showing the vibratory gyroscope accordingto a ninth example of the present invention;

FIGS. 29A, 29B, 29C and 29D are diagrams showing vibration modes of thevibrator according to the ninth example, in which FIG. 29A shows thedrive vibration mode, FIG. 29B shows the detection vibration mode of therotations about the X-axis, FIG. 29C shows the detection vibration modeof the rotations about the Y-axis, and FIG. 29D shows the detectionvibration mode of the rotations about the Z-axis;

FIGS. 30A and 30B are diagrams showing the polarizing directions and theconfiguration of the electrodes of the piezoelectric material formingthe vibrator according to the ninth example, in which FIG. 30A is across sectional view taken along line XXYA--XXXA of FIG. 28, and FIG.30B is a cross sectional view taken along line XXXB--XXXB of FIG. 28;

FIGS. 31A, 31B and 31C are side views showing the shape and structure ofthe added masses according to each example;

FIG. 32 is a perspective view showing a conventional vibratory gyroscopeusing a columnar vibrators; and

FIG. 33 is a view of explanatory showing the relationship between thedetection voltage from the piezoelectric device of the vibratorygyroscope and the Coriolis force.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a mass is added to a vibratorwhich is offset from a central axis of the vibrator. When the vibratoris vibrated in a first orthogonal direction perpendicular to the axisand rotated around an axis extending in a second orthogonal directionwhich is also perpendicular to the axis, the resulting Coriolis forceacts on the added mass in a direction parallel to the central axis andperpendicular to the first and second directions. Because the added massis offset from the central axis, the Coriolis force acts at a positiondeviated from the central axis of the vibrator. Therefore, the vibratoris deformed in the second direction due to the bending moment caused bythe Coriolis force.

If the Coriolis force acts in a direction parallel to the central axisof a plate-like vibrator, the vibrator is bendingly-vibrated due to theforegoing moment. By detecting the deformation (that is, eitherdeformation velocity or amount of deformation) caused from the bendingvibration, the angular velocity of the vibrator can be detected. If thevibratory gyroscope is formed from a plate member, one or more parallelgrooves may be formed in the plate member to form a plurality ofvibrators to which separate driving forces can be applied so as to causebending-vibrations the plurality of the vibrators in different phases bythe Coriolis force. In a case where one plate member is provided withthree parallel vibrators, the right and left vibrators and the centralvibrator can be vibrated in opposite phases. In this vibration mode, thestresses due to vibrations in the plate member can be balanced and,thus, stable vibrations can be generated. By changing the length of thecentral vibrator by trimming, the specific frequency can beset/adjusted. In the case where three vibrators are formed, the base ofthe plate member is rigidly supported in a cantilever method.

In the case where the added mass is provided and the vibrator isbending-deformed due to Coriolis force, the surface of the vibrator canbe placed in parallel to the surface of rotation (perpendicular to theaxis of rotation) of the rotating system for detecting the angularvelocity. Therefore, the vibratory gyroscope can be disposed efficientlyin a thin apparatus.

In the case where the added mass is provided for the vibrator having themajor (central) axis and, therefore, the Coriolis force acts in adirection deviated from the central axis of the vibrator andperpendicular to the central axis, the vibrator is torsionally vibrated.By detecting the torsional vibrations, the angular velocity can bedetected. By torsionally vibrating the vibrator in place ofbending-vibrating the same, the vibrator can be simply supported, forexample, at the central portion thereof. Also in the foregoing case, thecentral axis of the major axis can be placed with respect to the surfaceof rotation of the rotating system. Thus, an optimum structure for usein a thin apparatus can be realized.

That is, the vibratory gyroscope according to the present invention,which is capable of bending-deforming the plate-like vibrator or capableof torsionally-deforming the vibrator due to the added mass, is able todetect the angular velocity on the surface of rotation which is parallelto a substrate when the vibratory gyroscope is mounted in such a mannerthat its axis direction is in parallel to the substrate. On the otherhand, a vibratory gyroscope having no added mass and adapted to abending vibration mode as shown in FIG. 32 is only able to detect theangular velocity about an axis running parallel to the substrate if itis mounted in such a manner that its Z-axis is in parallel to thesubstrate. Therefore, if the vibratory gyroscope according to thepresent invention and provided with the added mass and thebending-vibration type vibratory gyroscope having no added mass andstructured as shown in FIG. 32 are, in parallel, mounted on a substrate,the angular velocity components in the two directions can be detected bythe two vibratory gyroscopes. Since all vibrators can be mounted inparallel to the substrate, a thin detection apparatus can be formedwhich is capable of detecting the two dimensional directions.Furthermore, an apparatus capable of detecting the angular velocity inthe three-dimensional directions and having a thin structure can beformed.

Assuming that the direction in which the vibrator is driven is the firstdirection, the vibratory gyroscope according to the present inventionhas the added mass disposed at a position deviated into the firstdirections. In a vibrator according to any of examples shown in FIGS.13, 16, 19 and 25 and vibrators of a first set (i) according to anexample shown in FIG. 28, the first direction, in which the vibrator isvibrated, is the X direction, and the added mass is disposed at aposition deviated to the X direction. Therefore, the vibrator isvibrated in the X direction, which is the first direction, due to theCoriolis force acting in the Y direction. The vibrator according to theexample shown in FIG. 22 and each of vibrators in a second set (ii)shown in FIG. 28, has the structure that the direction, in which thevibrator is vibrated, is the Z direction, and the added mass is disposedat a position deviated to the Z direction. Therefore, the vibrator isvibrated in the Z direction due to the Coriolis force acting in the Ydirection.

When the vibrator is driven to vibrate in a first direction (the X or Zdirection), the Coriolis force generated in the rotating system acts asa component in a direction perpendicular to the drive direction (thefirst direction). The present invention includes a structure such thatthe vibrator is vibrated in the first direction, which is the samedirection as the drive direction, due to the Coriolis force. Thus, theCoriolis force acting on the vibrator from a rotating system other thanthe rotating system to be detected is not detected as noise.

In the case where the vibrator is vibrated in the X direction as shownin FIG. 13, the added mass is disposed at a position deviated in the Xdirection with respect to the central axis of the vibrator. Thus, thevibrator is, due to the Coriolis force, vibrated in the X directionwhich is the same as the drive direction. By detecting the foregoingvibrations, rotations about the Z-axis can be detected. When rotationsabout the Y-axis are applied to the vibrator, the Coriolis forcegenerated due to the foregoing rotations acts in the Z direction, whichis perpendicular to the drive direction X. The component of the Coriolisforce in the X direction caused by rotation about the Y-axis is zero.Therefore, detection of only the vibrations in the X direction preventsdetection of the rotations about the Y-axis but enables only the angularvelocity due to the rotations about the Z-axis to be obtained.

As described above, according to the present invention, the angularvelocity in a desired rotating system is detected by making thedirection, in which the vibrator is vibrated, coincide with the drivedirection. Therefore, even if Coriolis force of an external rotatingsystem acts on the vibrator, the component of force of the Coriolisforce in the drive direction is zero. Thus, detection of a desiredrotating system can easily be performed.

The Coriolis force given in a rotating system about a predetermined axiscauses the vibrator to be vibrated in the first direction, which is thedrive direction. Furthermore, the Coriolis force of a rotating systemabout another axis causes the vibrator to be vibrated in the seconddirection which is perpendicular to the first direction. Therefore, byindividually detecting the vibrations of the vibrator in the firstdirection and those in the second direction, the Coriolis forcesrespectively given from rotating systems about two axis perpendicular toeach other can be detected.

The vibratory gyroscope may include one or more vibrators.

When a plurality of vibrators are provided and the vibrators aresymmetrically vibrated in the opposite amplitude directions, thevibrations for driving the vibrator and the vibrators for detection canbe stabilized. In the case where three parallel vibrators are integrallyformed from one elastic member and right and left vibrators and thecentral vibrator are vibrated in the opposite amplitudes, thesupport-side elastic member, in which the vibrator is not formed, is notaffected by the vibrations and the portion can be stabilized. Therefore,the base of the elastic member can be supported by a rigid (cantilever)method. Thus, a simple structure may be used to support the vibratorygyroscope.

As described above, one vibrator or vibrators in one set are able todetected Coriolis forces and angular velocities in a rotating systemabout two axes. However, one vibrator or vibrators in one set cannotdetect Coriolis forces in each of rotating systems about three axes. Thereason for this is that although the Coriolis force can be obtained ascomponents of the perpendicular Y and Z directions that areperpendicular to the X direction in a case where the vibrator isvibrated in the X direction, the component of the Coriolis force in theX direction, which is the same direction as the drive direction, isalways zero. That is, only the Coriolis force as the components in thetwo axial directions except the direction, in which the vibrator isvibrated, can be detected.

In order to detect the respective components of all Coriolis forces inthe rotating systems about the three axes, two sets of vibrators arerequired. In the case where two sets of vibrators are provided as shownin FIG. 28, the vibrators of a first set (i) and vibrators of a secondset (ii) have added masses disposed in different directions. Forexample, the vibrators of the first set (i) have the added massesdeviated in the X direction, whereas the vibrators of the second set(ii) have the added masses deviated in the Z direction. The vibratorsare respectively driven in the same directions as the directions inwhich the added masses are deviated. The vibrations of the vibrators ofthe first set in the X direction enable the rotational component aboutthe Z-axis to be detected. The vibrations of the vibrators of the secondset in the Z direction enable the rotational component about the X axisto be detected. If rotations about the Y-axis, which is the direction ofthe major axis of the vibrator, are given, the vibrators in the firstset (i) and those in the second set (ii) are vibrated in the Zdirection. Thus, by detecting vibrations of the vibrators in at leastone set in a direction perpendicular to the drive direction, therotational component about Y-axis can be detected.

In the case where two sets of vibrators are provided, either setcomprises three vibrators as shown in FIG. 19 and a residual setcomprises three vibrators as shown in FIG. 22 so that the rotationalcomponent about the three axes are detected.

If the vibrator is made of a single crystal material, the temperaturecoefficient of the frequency (change in the frequency due to change inthe temperature) can be made substantially zero. Thus, influence ofchange in the temperature upon the accuracy in detection can beeliminated satisfactorily.

The added mass mO provided for the vibrator may be formed by bonding anindividual member to a leading portion of the vibrator, as shown in FIG.31A. As a result, the center of gravity G can be deviated with respectto central axis O--O of the vibrator (a neutral axis of the vibratoralone, that is, without considering the added mass). The added mass mOmay be formed integrally with the leading portion of the vibrator bycausing the same to project or by bending the same, as shown in FIG.31B. As an alternative to this, a cut portion may be formed in theleading portion of the vibrator as shown in FIG. 31C to form theresidual portion to serve as the added mass mO. Also in the foregoingcase, the center of gravity G is, in the leading portion of thevibrator, deviated from the central axis O--O of the vibrator.

Embodiments of the present invention will now be described withreference to the drawings.

First Embodiment

FIG. 1 is a perspective view showing a vibratory gyroscope according toa first embodiment of the present invention. FIG. 2A is a side viewshowing the operation in a vibration mode in which the vibratorygyroscope shown in FIG. 1 is vibrated due to the Coriolis force. FIG. 2Bis a view of explanatory showing a state where the vibratory gyroscopeis bending vibrated in a secondary resonance mode, and FIG. 3 is anenlarged cross sectional view taken along line III--III of FIG. 1showing the structure of the piezoelectric devices mounted on thevibratory gyroscope of the first embodiment.

The vibratory gyroscope shown in FIG. 1 includes a single flat vibrator11 rigidly connected at a first end to a support member 12 such that thevibrator 11 is supported using a cantilever method (a rigid supportmethod). The vibrator 11 is made of an isoelastic metal (Elinvar). Theisoelastic metal (Elinvar) is a material in which the Young's modulus isnot substantially changed in response to temperature changes in a rangeapproximately equal to room temperature. The isoelastic metal (Elinvar)is an alloy consisting of Fe (iron), Ni (nickel), Cr (chrome) and Ti(titanium) or an alloy further comprising Co (Cobalt).

An added mass (protrusion) mO is disposed on the upper side surfacealong the leading (free) edge of the vibrator 11 and protrudes from thevibrator 11 (alternatively, the added mass mO may be disposed on thelower side surface of the vibrator 11). The added mass mO may beseparately formed and secured to the vibrator 11 using, for example, anadhesive. In this case, the added mass mO may be formed from a metalhaving a larger density than that of the isoelastic material of thevibrator 11. Alternatively, the added mass mO and the vibrator 11 may beformed integrally

FIGS. 1 and 2 show a central (longitudinal) axis O of the vibrator 11.The central axis O is a line passing through the center of gravity ofthe vibrator 11 and extends in the Y-axis direction. The central axis Ois a neutral axis of the vibrator 11 during deflection (vibration). Inthis embodiment, an assumption is made that the Coriolis force acts inthe Y direction, that is, parallel to the central axis O. Therefore, theadded mass mO disposed on either (upper or lower) side surface of theleading portion of the vibrator 11 causes application point O1 of theCoriolis force to be located above the central axis O (as shown in FIG.2), or below the central axis O (when the added mass is located on thelower side surface). Because the application point O1 is displaced fromthe central (neutral) axis O, the Coriolis force produces a bendingmoment at the free end of the vibrator 11, thereby causing the free endof the vibrator 11 to vibrate in the Z-direction (i.e., in the Y-Zplane, as shown in FIG. 2A).

As shown in FIG. 1, piezoelectric devices 14 and 15 serving as drivemeans are secured along opposite side edges of the vibrator 11 andextend in the Y-axis direction. As shown in FIG. 3, the piezoelectricdevices 14 and 15 are disposed symmetrically on the upper and lowersurfaces of the vibrator 11. A driving electrode layer 17 is formed oneach surface of the piezoelectric devices 14 and 15 on the upper andlower sides of the vibrator 11. The electrode layers 17 and the vibrator11 supply AC voltage to each of the piezoelectric devices 14 and 15 inthe thickness direction of the vibrator 11 (in the Z direction).

As shown in FIG. 3, a piezoelectric device 16 serving as a detector issymmetrically secured on a central portion of the upper and lowersurfaces of the vibrator 11. A detection electrode layer 18 is formed oneach surface of the piezoelectric devices 16 which is used to detect thepotential difference across the piezoelectric devices 16, measured inthe thickness direction of the vibrator 11 (in the Z direction), whichis generated due to dielectric polarization of the piezoelectric devices16.

For purposes of explaining the directions of dielectric polarization(indicated by the arrows in FIG. 3), the piezoelectric devices 14, 15and 16 are shown in FIG. 3 as being thicker than their actual thickness.

The drive means include a structure such that the polarizing directionsof the piezoelectric devices 14 disposed on the upper and lower sidesurfaces of the vibrator 11 oppose each other in the Z direction.Likewise, the piezoelectric devices 15 disposed on the upper and lowerside surfaces of the vibrator 11 have opposite polarizing directions,which are opposite in direction to the polarizing directions of thepiezoelectric devices 14. The piezoelectric devices 16 disposed on theupper and lower surfaces of the vibrator 11 have the same polarizingdirection (for example, as shown in FIG. 3, the polarizing direction isin the -Z direction). The vibrator 11 is electrically grounded, therebyserving as an opposite electrode with respect to each of the electrodelayers 17 and 18.

The operation of the vibratory gyroscope according to the firstembodiment will now be described.

AC voltage having a predetermined frequency is applied from a drivecircuit to the electrode layers 17 of the piezoelectric devices 14 and15 disposed on the upper and lower side surfaces of the vibrator 11. Inthe case in which the polarizing directions of the piezoelectric devices14 and 15 are as shown in FIG. 3, an AC voltage having the same phase isapplied to the electrode layers 17 on the both surfaces of thepiezoelectric devices 14 and 15.

When the piezoelectric devices 14 and 15 are applied with the foregoingAC voltage, contraction and expansion of the piezoelectric devices 14and 15 cause the free end of the vibrator 11 to be vibrated (deformed)in the X direction (in the X-Y plane). If the vibrator 11 issubsequently rotated about the Z-axis, Coriolis force acts on thevibrator 11 and added mass mO in the Y direction (that is, perpendicularto the X direction). Because the added mass mO is displaced (above) thecentral axis O, the Coriolis force is applied at point Oh of the addedmass mO, which is deviated from the central axis O. The resulting momentproduced by the Coriolis force causes the free end of the vibrator 11 tobe bent (vibrated) in the Z direction (in the Y-Z plane).

If, at a certain moment, the piezoelectric device 14 exhibits expandingforce in the Y direction and the piezoelectric device 15 exhibitscompressive force in the Y direction (as shown in FIG. 1), the directionof the drive deformation of the vibrator 11 is made to be in the +Xdirection. If the direction of the drive deformation of the vibrator 11is in the +X direction and the vibrator is rotated about the Z-axis,Coriolis force acts in the +Y direction. As a result, the vibrator 11 isbending-deformed in a direction indicated by Oa shown in FIG. 2A. If thepiezoelectric device 14 exhibits the compressive force in the Ydirection and the piezoelectric device 15 exhibits the expansion forcein the Y direction, the direction of the resulting drive deformation ofthe vibrator 11 is in the -X direction. In the foregoing case, theCoriolis force acts in the -Y direction, and thus the vibrator 11 isdeformed in a direction indicated by Ob shown in FIG. 2A.

The bending vibration of the vibrator 11 in the Z direction is detectedby the piezoelectric devices 16 disposed on the two sides of thevibrator 11. When the vibrator 11 is, by the Coriolis force, bent in the+Z direction, the piezoelectric device 16 disposed on the lower surfaceof the vibrator 11 is stretched (expanded) in the Z direction, in acertain vibration phase. On other hand, the piezoelectric device 16 onthe upper surface of the vibrator 11 is compressed in the Z direction.In the case where the polarizing direction of the piezoelectric device16 is as shown in FIG. 3, AC voltages having the same phase can beobtained at the piezoelectric devices 16 disposed on the two sides ofthe vibrator 11 and the detection electrode layer 18. By adding thevoltages from the electrode layers of the piezoelectric devicesrespectively disposed on the two sides of the vibrator 11, AC voltagecorresponding to the bending vibration of the vibrator 11 in the Zdirection can be obtained. In accordance with the thus-obtained ACvoltage, the angular velocity ω about the Z-axis can be determined.

When the Coriolis force acts on the application point O1 and thus thevibrator 11 is bending-vibrated in the Z direction, there arises thefollowing three cases: the vibrator 11 is bent/vibrated in a primaryresonance mode as indicated by Oa and Ob shown in FIG. 2A, the vibrator11 is bent/vibrated in a secondary resonance mode as indicated by Ocshown in FIG. 2B, and the vibrator 11 is vibrated in a higher resonancemode. When the vibrator 11 is driven in the X direction, the vibrator 11is vibrated in the primary resonance mode. Although the bendingvibration mode of the vibrator 11 in the Z direction is affected by thefrequency of the resonant vibration of the vibrator 11 in the Xdirection, the bending vibration in the Z direction is usually thesecondary resonance mode shown in FIG. 2B in the case where the vibrator11 is driven in the resonance mode in the X direction.

FIG. 4 shows a modification of the vibratory gyroscope according to thefirst embodiment shown in FIG. 1.

The vibratory gyroscope shown in FIG. 4 includes a flat member 10 madeof isoelastic metal (Elinvar) in which a groove 11c is formed by cuttingthe leading portion of the flat member 10. Thus, two flat, parallelvibrators 11a and 11b separated from each other by the groove 11c areformed. The two vibrators 11a and 11b have the same shape anddimensions. Furthermore, each of the vibrators 11a and 11b includes anadded mass mO on either side in the leading portion (free end) thereofby means of adhesion or the like.

Similar drive means and detection means to those of the vibrator 11shown in FIG. 1 are provided for the vibrators 11a and 11b. Each of thevibrators 11a and 11b has piezoelectric devices 14 and 15. Note that thepiezoelectric devices 14 and 15 of the vibrators 11a and 11b aredisposed at different positions from those of the vibrator 11 shown inFIG. 1. Each of the vibrators 11a and 11b has the piezoelectric devices14 on the two sides thereof at positions near the groove 11c. On theother hand, piezoelectric devices 15 are secured at ends of the twosides of the flat member 10, the ends opposing the groove 11c. Thedielectric polarization directions of the piezoelectric devices 14 and15 shown in FIG. 4 are the same as those shown in FIG. 3.

In the central portion of the two sides of the vibrator 11a, there issecured piezoelectric devices 16 serving as detection means. Thedielectric polarization direction of the piezoelectric devices 16 is thesame as that of the piezoelectric device 16 shown in FIG. 1. Similarly,the vibrator 11b has piezoelectric devices 16a on the opposing sidesthereof to serve as detection means. The dielectric polarizationdirection of the piezoelectric devices 16a disposed on the two sides ofthe vibrator 11b opposes that of the piezoelectric devices 16 shown inFIG. 3. That is, the polarizing directions of both of the piezoelectricdevices 16a disposed on the two sides of the vibrator 11b commonly arein the +Z direction.

In the vibratory gyroscope shown in FIG. 4, the vibrators 11a and 11bare, by the piezoelectric devices 14 and 15 serving as the drive means,deformation-vibrated in the X direction. Since the positions of thepiezoelectric devices 14 and 15 of the vibrators 11a and 11b oppose eachother in the X direction, the vibrators 11a and 11b vibrate in oppositephases. For example, if the direction of amplitude of the vibrator 11ais in the +X direction in a certain phase, the direction of amplitude ofthe vibrator 11 is in the -X direction.

When the flat member 10 is placed in a rotating system which is rotatedabout the Z-axis, Coriolis force in the Y direction acts on the flatmember 10. Since the phases of the vibration deformation in the Xdirection are opposite to each other between the vibrators 11a and 11b,the phase of the Coriolis forces acting on the vibrator 11a and thatacting on the vibrator 11b also oppose each other. If the direction ofamplitude of the vibrator 11a is in the +X direction and the directionof amplitude of the vibrator 11b is in the -X direction, the Coriolisforce acting on the vibrator 11a is in the +Y direction and that actingon the vibrator 11b is in the -Y direction.

Since the added mass mO is secured to each of the leading portions ofthe vibrators 11a and 11b, the Coriolis force acts on the applicationpoint O1 which is deviated to the upper side of the drawing with respectto the central axis O of each of the vibrators 11a and 11b. As a result,the vibrator 11a, on which the Coriolis force in the +Y direction acts,is bent/deformed in the -Z direction, as shown in FIG. 5. On the otherhand, the vibrator 11b, on which the Coriolis force in the -Y directionacts, is bending-deformed in the +Z direction. Thus, the two vibrators11a and 11b alternately vibrate in the Z direction in such a manner thatthe phases of the vibrations are opposite to each other.

The bending vibrations are detected by the piezoelectric devices 16 and16a provided for the corresponding vibrators 11a and 11b. Although thevibrators 11a and 11b bending-vibrate in the Z direction in the oppositephases, the fact that the polarizing directions of the piezoelectricdevices 16 and 16a are opposite to each other enables the same-phasevoltage to be obtained from the detection electrode layers 18 of the twopiezoelectric devices 16 and 16a. By adding the thus-obtained voltages,the angular velocity ω about the Z-axis can be detected.

The vibratory gyroscope shown in FIG. 4 may have a structure such thateither of the added masses mO is disposed in the upper portion of thedrawing sheet in the leading portion of the vibrator 11a and the addedmass mO is disposed in the lower portion of the drawing sheet in theleading portion of the vibrator 11b. In the foregoing case, the twovibrators 11a and 11b are deformation-vibrated in the X direction in thesame phase. That is, the vibrators 11a and 11b are driven in such amanner that both of the directions of amplitude of the vibrators 11a and11b are in the +X direction or the -X direction at a certain moment. Inthe foregoing case, Coriolis forces in the same phase acts on the twovibrators 11a and 11b in the Y direction. Both of the Coriolis forcesacting on the vibrators 11a and 11b at a certain moment are in the +Ydirection or the -Y direction

However, the structure, when the added masses mO provided for thevibrators 11a and 11b are disposed to oppose each other with respect tothe central axis O, the vibrators 11a and 11b are respectivelybending-vibrated in the -Z direction and the +Z direction in oppositephases. As a result, the same vibration mode as that shown in FIG. 5 isrealized. Therefore, the piezoelectric devices 16 and 16a serving as thedetection means are able to detect the bending vibration components,similar to the structure shown in FIG. 4.

The modification shown in FIG. 4 is usually structured such that thevibrations of the vibrators 11a and 11b in the X direction are in theprimary resonance mode and those in the Z direction are in the secondaryresonance mode shown in FIG. 2B.

FIG. 6 shows another modification of the first embodiment. The vibratorygyroscope shown in FIG. 6 comprises a flat plate 10a made of isoelasticmetal (Elinvar) and having two parallel grooves 11g and 11h formed bycutting the flat plate 10a from its leading portions. Thus, three flatvibrators 11d, 11e and 11f separated from one another by the groves 11gand 11h are produced. The vibrators 11d, 11e and 11f have the same shapeand dimensions. Note that the central vibrator 11f and the right andleft vibrators 11d and 11e have different widthwise directions in the Xdirection. The vibrators 11d, 11e and 11f have, on the same sides,corresponding added masses mO in their leading portions.

On the two sides of the right and left vibrators 11d and 11e, there aredisposed piezoelectric devices 14 and 15 serving as the drive means.Furthermore, piezoelectric devices 16 serving as the detection means aresecured to the central portions of the two sides of the vibrators 11dand 11e. The configuration of the piezoelectric devices 14, 15 and 16 isthe same as those provided for the vibrator 11 shown in FIG. 1 and asthose provided for either of the vibrator 11a shown in FIG. 4. That is,the polarizing direction of the piezoelectric devices 14, 15 and 16provided for the vibrators 11d and 11e is the same as those of thestructure shown in FIG. 3.

On the two sides of the vibrator 11f, which is disposed in the centralportion of the flat plate 10a, there are disposed piezoelectric devices14 and 15 serving as the drive means in such a manner that theX-directional configuration opposes the configuration in the vibrators11d and 11e. That is, the piezoelectric devices 14 are secured on thetwo sides near the groove 11g and the piezoelectric devices 15 aresecured to the two sides near the groove 11h. Furthermore, piezoelectricdevices 16a serving as the detection means are secured to the two sidesof the vibrator 11f. That is, the configuration of the piezoelectricdevices 14, 15 and 16a provided for the central vibrator 11f is the sameas those provided for the other vibrator 11b shown in FIG. 4.

When the electrode layers 17 of the piezoelectric devices 14 and 15 ofthe vibratory gyroscope shown in FIG. 6 are applied with AC voltages,the vibrators 11d, 11e and 11f are deformed/vibrated in the X directionin the flat plate 10a. The configuration of the driving piezoelectricdevices 14 and 15 in each of the vibrators 11d, 11e and 11f causes theright and left vibrators 11d and 11e to be deformation-vibrated in the Xdirection in the same phase. On the other hand, the central vibrator 11fis deformation-vibrated in the X direction in the opposite phases. Ifthe amplitudes of the right and left vibrators 11d and 11e are in the +Xdirection, the amplitude of the central vibrator 11f is in the -Xdirection.

When the flat plate 10a is placed in a rotating system about the Z-axis,Coriolis forces in the same direction, that is, in the Y direction, acton the right and left vibrators 11d and 11e. On the other hand, Coriolisforce in the opposite direction acts on the central vibrator 11f. If theright and left vibrators 11d and 11e are deformed in the +X directionand the central vibrator 11f is deformed in the -X direction at acertain moment, as shown in FIG. 6, the Coriolis forces act on the rightand left vibrators 11d and 11e in the +Y direction and it acts on thecentral vibrator 11f in the -Y direction.

Since the added mass mO is disposed in each of the leading portions ofthe vibrators 11d, 11e and 11f, the Coriolis force acts on each of theapplication points O1 which are, as shown on the drawing sheet, deviatedupwards with respect to the central axis O of each of the vibrators 11d,11e and 11f. The moment generated due to the Coriolis force that acts asdescribed above causes the right and left vibrators 11d and 11e and thecentral vibrator 11f to deformation-vibrate in the Z direction in theopposite phases. As shown in FIG. 7, in a certain phase, both of theamplitudes of the bending vibrations of the right and left vibrators 11dand 11e are in the -Z direction, and the amplitude of the bendingvibrations of the central vibrator 11f is in the +Z direction. That is,the Coriolis force causes the vibrators 11d and 11e to bending-vibratein the same direction, that is, in the Z direction, and the centralvibrator 11f to bending-vibrate in the alternate phases to the phases ofthe bending vibrations of the vibrators 11d and 11e. Thebending-vibrations in the Z direction are in the primary resonance modeshown in FIG. 2A, in the secondary resonance mode shown in FIG. 2B or ina higher vibration mode.

Since the detection piezoelectric devices 16 are disposed on the twosides of the right and left vibrators 11d and 11e and the detectionpiezoelectric devices 16a are disposed on the two sides of the centralvibrator 11f, addition of the detected voltages obtained from theelectrode layers 18 on the surfaces of the piezoelectric devices 16 and16a enables the angular velocity ω about the Z-axis to be detected.

The flat plate 10a shown in FIG. 6 may have a structure such that addedmasses mO are disposed on the upper surfaces in the leading portions ofthe right and left vibrators 11d and 11e and added mass mO is, in theleading portion of the central vibrator 11f, disposed in the lowersurface that opposes the foregoing upper surface.

In the foregoing case, the X-directional configuration of thepiezoelectric devices 14 and 15 serving as the drive means is made to becommonly for all vibrators 11d, 11e and 11f. In this case, thepiezoelectric devices 14 and 15 serving as the drive means cause allvibrators 11d, 11e and 11f to be deformation-vibrated in the X directionin the same phase. That is, the X-directional amplitudes of allvibrators 11d, 11e and 11f are in the +X direction or the -X directionat a certain moment.

In the foregoing case, the Coriolis forces generated due to the rotatingsystem about the Z-axis act on all vibrators 11d, 11e and 11f in thesame direction. That is, the Coriolis forces act on all vibrators 11d,11e and 11f in the +Y direction or the -Y direction. Since the addedmass mO of the central vibrator 11f and the added masses mO of the rightand left vibrators 11d and 11e are disposed on the opposite two sides,the Coriolis forces in the same direction cause the right and leftvibrators 11d and 11e to be bending-vibrated in the Z direction in thesame phase. On the other hand, the central vibrator 11f is caused to bebending-vibrated in the Z direction in the opposite phase. Thus, thevibration mode that is the same as that shown in FIG. 7 can be realized.

Also in the foregoing case, the AC voltages obtained from the electrodelayers on the surfaces of the piezoelectric devices 16 and 16a servingas the detection means enable the angular velocity ω to be determined.

Since the vibratory gyroscope shown in FIG. 6 is able to detect thebending vibrations generated due to the Coriolis forces from the threevibrators 11d, 11e and 11f, the level of detection output can be raised.

Since the right and left vibrators 11d and 11e and the central vibrator11f are, in the vibratory gyroscope shown in FIG. 6, bending-deformed inthe Z direction in the alternate phases, the quantity of deformation ofa base portion (portion a) of the flat plate 10a, in which the grooves11g and 11h are not formed, is very small. Thus, the flat plate 10a canbe supported in a rigid manner such that the flat plate 10a is held fromthe two sides by the support member 12. That is, even if the flat plate10a is supported in the rigid manner, the vibration mode shown in FIG. 7is not affected. If the length of the central vibrator 11f of the flatplate 10a shown in FIG. 6 is changed, the resonant frequency (specificfrequency) of the vibration mode shown in FIG. 7 can be adjusted. Thus,the operation for adjusting the frequency can be performed very easily.

Each of the vibratory gyroscopes respectively shown in FIGS. 1, 4 and 6is able to detect the angular velocity about the axis in the direction(the Z direction) perpendicular to the surface (which lies in the X-Yplane) of the flat-shape vibrator.

Therefore, by mounting any of the vibratory gyroscopes in such a mannerthat its surface runs parallel to a substrate, the angular velocity in arotating system that is in parallel to the substrate can be detected.

By employing another vibratory gyroscope for detecting the angularvelocity of a rotating system about the Y-axis, the rotational componentin each of the two or three dimensional directions can be detected.

For example, each added mass mO is omitted from a vibratory gyroscopecomprising the flat plate 10a shown in FIG. 6. In the foregoinggyroscope, the right and left vibrators 11d and 11e and the centralvibrator 11f similarly to the gyroscope shown in FIG. 6, vibrated in thedirection of the surface of the flat plate 10a (the X direction) in theopposite phases. If the foregoing gyroscope is placed in a rotatingsystem about the Y-axis, the Coriolis forces causes the vibrators 11d,11e and 11f to be bending-vibrated in the Z direction. The bendingvibration modes of the vibrators 11d, 11e and 11f are the same as thoseshown in FIG. 7. By detecting the bending vibrations, the angularvelocity about the Y-axis can be detected.

Therefore, a thin detection apparatus for detecting angular velocitiesaround two axes may be produced using the vibratory gyroscope shown inFIG. 6 and a modified version of the vibratory gyroscope shown in FIG. 6(having no added mass mO) by mounting the two vibratory gyroscopes on asubstrate in such a manner that their surfaces are in parallel to thesubstrate. The thus-formed detection apparatus is able to detect theangular velocities about the Z-axis and the Y-axis, and as well as ableto detect the rotation in each of the two-dimensional directions. Sincethe surface of the flat vibrator of either vibrator is in parallel tothe substrate, a thin detection apparatus can be realized.

Second Embodiment

FIG. 8 is a perspective view showing a second embodiment of thevibratory gyroscope according to the present invention. FIG. 9,consisting of 9A and 9B, shows the operation of the vibratory gyroscopeaccording to this embodiment, in which FIG. 9B is a plan view and FIG.9B is a side view.

The vibratory gyroscope according to this embodiment comprises avibrator 20 having a rectangular (or square) cross sectional shape. Thevibrator 20 is formed by isoelastic metal (Elinvar). In FIGS. 9A and 9B,the central axis (an axis passing through the center of gravity of therectangular cross section) of the vibrator 20 is indicated by O.

The vibrator 20 is supported by paired support rods 21 at two points onthe central axis O. The support rods 21 are secured at the lower surfaceof the vibrator 20 at the same distance from the center of the centralaxis O, the support rods 21 having lower ends that are secured to thesubstrate or the support plate.

At the two ends of the major axis (the central axis O) of the vibrator20, there are formed added masses mO. The added masses mO are in theform of cut portions 20b formed by cutting the two ends of the vibrator20. Since the added masses mO are formed as shown in FIG. 9B, Coriolisforces acting in the Y direction act on the application points 11a and11b that are deviated with respect to the central axis O.

As shown in FIG. 9A, the vibrator 20 has, on the two sides thereof thatoppose the X direction, piezoelectric devices 22 secured thereto toserve as the drive means. In FIG. 9A, the piezoelectric devices 22 areshown to be thicker than their actual thickness in order to indicatetheir dielectric polarization directions (indicated by arrows). Thepolarizing directions of the piezoelectric devices 22 are in the samedirection (e.g., downward in FIG. 9A). The piezoelectric devices 22 havedrive electrode layers 23 on the surfaces thereof.

The vibrator 20 has, on the upper and lower sides thereof thatperpendicular to the Z direction, piezoelectric devices 24 securedthereto to serve as detection means. In FIG. 9B, the piezoelectricdevices 24 are shown to be thicker than the actual thickness thereof andtheir dielectric polarization directions are indicated by arrows. Thepolarizing directions of the two piezoelectric devices 24 on the upperand lower sides of the vibrator 20 are the same, for example, in the -Zdirection. The piezoelectric devices 24 have detection electrode layers25 on the surfaces thereof.

Note that the vibrator 20 serves as opposite electrode to the two driveelectrode layers 23 and 25, the vibrator 20 being electrically grounded.

The operation of the vibratory gyroscope according to the secondembodiment will now be described.

In the vibratory gyroscope according to this embodiment, AC drivingvoltages are applied to the drive electrode layers 23 of thepiezoelectric devices 22. The electrode layers 23 are applied with ACvoltages in the same phase, thus resulting in that the vibrator 20 is sodriven that it is bending vibrated in the X direction while using, asthe nodes, the two support points formed by the support rods 21. FIGS.9A and 9B show a case where the vibrator 20 is bending-vibrated in theprimary resonance mode. As shown in FIG. 9A by the dash-and-dot line Od,the direction of the amplitude of the central axis O at a certain momentis such that the right end when viewed in the drawing is the +Xdirection and the left end is the -X direction.

When the vibrator 20 is placed in a rotating system about the Z-axis,Coriolis force in the outward direction (the +Y direction) of the radiusof rotation acts on the right end of the vibrator 20 when viewed in thedrawing sheet. On the other hand, Coriolis force in the inward direction(the -Y direction) acts on the left end of the vibrator 20 when viewedin the drawing sheet.

Since added masses mO are formed at the two ends of the major axis ofthe vibrator 20, the Coriolis forces in the +Y direction and the -Ydirection act on the application points O1a and O1b which are deviatedvertically in the opposite directions with respect to the central axisO. The moments of the Coriolis forces acting on the deviated positionscause the vibrator 20 to be vertically bending-vibrated in the primaryresonance mode. FIG. 93 shows, with the dash-and-dot line Oe, the stateof deflection of the central axis O at a certain moment.

The vibrations of the vibrator 20 in the mode indicated by line Oegenerated due to the Coriolis forces are detected by the piezoelectricdevices 24 serving as the detection means. When the vibrator 20 isdeformed in the phase indicated by line Oe in the state shown in FIG.9B, the piezoelectric device 24 on the upper surface is contracted onthe Y-axis, and the piezoelectric device 24 on the lower surface isextended on the Y-axis. By adding the voltages generated on theelectrode layers 25 of the piezoelectric devices 24 due to the opposingoperations of the piezoelectric devices 24, the angular velocity ω aboutthe Z-axis can be determined.

FIGS. 10A and 10B show a state where the vibrator 20 of the vibratorygyroscope similar to that shown in FIG. 8 is vibrated in the secondaryresonance mode in the driving direction and the detection direction.FIG. 10A is a plan view, and FIG. 10B is a side view.

The vibrator 20 has individual added masses mO secured thereto at thetwo vertical ends at the two ends in the major direction (the Ydirection) thereof. That is, the added masses may be in the form of thecut portions 20b as shown in FIG. 8 or the same may be formed bysecuring individual members as shown in FIG. 10.

FIG. 10A shows the piezoelectric devices 22 serving as drive means anddriving electrode layers 23, the polarizing directions of thepiezoelectric devices 22 secured to the four portions being as indicatedby arrows. When AC voltages in the same phase are applied to theelectrode layers 23, the vibrator 20 bending-vibrates in the secondaryresonance mode in such a manner that its central axis deforms as shownby line Of at a certain moment. As a result, Coriolis forces in the samedirection in the direction of the radius of rotation acts on the twoends of the vibrator 20.

The added masses mO are secured to the two ends of the vibrator 20 inthe major axis thereof so that Coriolis forces acts on the applicationpoints O1a and O1b which are deviated in the Z direction with respect tothe central axis O. As a result, the central axis O of the vibrator 20,as shown in FIG. 10B, bending-vibrates in the secondary resonance modeas indicated by line Og. The piezoelectric devices 24 serving as thedetection means and the electrode layers 25 are shown in FIG. 10B, andthe polarizing directions of the piezoelectric devices 24 are asindicated by arrows. The bending vibrations in the mode indicated byline Og shown in FIG. 10B are detected as voltages from the electrodelayers 25 so that the angular velocity ω of the rotating system aboutthe Z-axis is obtained.

Third Embodiment

FIG. 11 shows a third embodiment of-the vibratory gyroscope according tothe present invention.

In this embodiment, a vibrator 30 includes an isoelastic metal barhaving a rectangular cross sectional shape which is supported by asupport member 31 in a cantilever method. Furthermore, an added mass mOis secured on the upper surface of the leading portion (free end) of thevibrator 30 (i.e., the added mass protrudes in the Z direction). Theadded mass mO may be formed by cutting the leading portion of thevibrator 30 as shown in FIG. 8.

The vibrator 30 includes piezoelectric devices 33, which serve as thedrive means, which are disposed opposite sides thereof such thatrepeated extension and contraction of the vibrator 30 in the Y directionproduces vibration of the free end in the Y direction. FIG. 11 shows astate where the vibrator 30 extends in the +Y direction at a certainphase.

When the vibrator 30 is placed in the rotating system about the Z-axis,Coriolis force in the X direction acts on the vibrator 30. Since theadded mass mO is disposed in the leading portion of the Vibrator 30, theCoriolis force in the X direction acts on the central axis O of thevibrator 30 at a position deviated in the +Z direction. As a result, thevibrator 30 generates torsional vibrations in direction O about thecentral axis O extending in the Y direction. When the vibrator 30extends in the +Y direction in a certain phase as shown in FIG. 11,Coriolis force in the -X direction acts on the added mass mO and thevibrator 30 is torsionally deformed in the direction -θ.

The extending and contracting vibrations of the vibrator 30 in the Ydirection causes the vibrator 30 to be alternately torsionally vibratedin the directions of +θ and -θ. The foregoing torsional vibrations canbe detected as the voltages from the electrode layers of thepiezoelectric devices 34 and 35 disposed on the upper and lower surfacesof the vibrator 30 that oppose the Z direction. When the vibrator 30 istorsionally deformed in the direction +θ for example, either of thepiezoelectric device 34 generates deflection in such a manner that itsleading portion faces the +Z direction, while the piezoelectric device35 generates deflection in such a manner that its leading portion facesthe -Z direction. The deflections in the different directions enable thedeformation caused from the torsional vibrations of the vibrator 30 tobe detected. Thus, the angular velocity ω in a rotating system about theZ-axis can be detected.

FIG. 12 shows a modification of the third embodiment of the presentinvention.

In this modification, a support rod 21 is secured to the lower surfaceat a central position of the major axis of the vibrator 30 having arectangular cross section so that the central portion of the vibrator 30is simply supported by the support rod 36. Deviated masses mO aredisposed at the two ends of the vibrator 30. The added masses mO areformed by securing individual metal members or the like to the vibrator

The piezoelectric device 33 serving as the drive means similarly to thatshown in FIG. 11 vibrates the vibrator 30 in such a manner that thevibrator 30 contracts and extends in the Y direction. When the vibrator30 is placed in a rotating system about the Z-axis, Coriolis force inthe X direction acts on the vibrator 30. Since the added masses mO aredisposed, the Coriolis force acts on the central axis O of the vibrator30 at a position deviated in the Z direction. As a result, the vibrator30 generates torsional vibrations.

When the vibrator 30 is extends and deformed at a certain-moment asshown in FIG. 12 for example, the two ends of the major axis of thevibrator 30 have a velocity component in the +Y direction with respectto the direction of rotation. As a result, an end of the vibrator 30 istorsionally deformed in the -θ direction and another end of the same istorsionally deformed in the +θ direction. Thus, the overall body of thevibrator 30 is torsionally vibrates about the central axis O. Thetorsional vibrations are detected by the piezoelectric devices 34 and 35serving as detection means similar to those shown in FIG. 11. Thevibratory gyroscope using the torsional vibrations shown in FIGS. 11 and12 may comprise a vibrator having a rectangular, a square cross sectionor a round-rod vibrator 30 having a circular cross section.

In the second embodiment shown in FIGS. 8 to 10 and the third embodimentshown in FIGS. 11 and 12, the direction of the major axis of thevibrator is in the Y direction to enable the angular velocity about theZ-axis (perpendicular to the direction of the major axis) to bedetected. Therefore, if each vibrator is mounted on a substrate in sucha manner that the direction of its major axis runs parallel to thesubstrate, the angular velocity of the rotating system on a planerunning parallel to the surface of the substrate can be detected. Theconventional structure shown in FIG. 32 is able to detect the angularvelocity about the major axis of the vibrator. Therefore, when thevibrator 30 of the vibratory gyroscope according to the secondembodiment or the third embodiment is mounted in such a manner that itsmajor axis runs parallel to the surface of the substrate and as well asthe conventional vibratory gyroscope shown in FIG. 32 is mounted in sucha manner that its direction of the major axis runs parallel to thesubstrate, a detection apparatus can be formed which has a thinstructure and which is capable of detecting both angular velocity on therotational plane running parallel to the substrate and the angularvelocity on the rotational surface perpendicular to the substrate.

In the embodiment shown in FIGS. 8 to 10 and that shown in FIG. 12, thecentral portion of the vibrator is simply supported by a support rod.The foregoing structure is not suitable to be supported in a rigidmanner, contrary to the structure shown in FIG. 6. The structure thatthe central portion of the vibrator is supported by the support rod isable to significantly simplify the supporting conditions. Furthermore,an advantage can be obtained in that the structure for supporting thevibrator on a substrate or the like can be simplified.

As shown in numerical expression 1, the Coriolis force F is inproportion to the angular velocity A. In each of the foregoingembodiments, the bending vibrations and torsional vibrations of thevibrator generated due to the Coriolis force F can be detected as the ACvoltages from the electrode layers of the piezoelectric devices servingas the detection means. In accordance with the AC voltages, the angularvelocity ω can be calculated. The principle of the detection is shown inFIG. 33.

The voltage obtained from the electrode layer of the piezoelectricdevice provided for each vibrator and serving as the detection means isindicated by vector VO shown in FIG. 33 V1 indicates the leak outputvoltage when the vibrator is not rotated, and the voltage detected inaccordance with the Coriolis force, which is in proportion to theangular velocity ω, when the vibrator is rotated, is indicated by V2.Furthermore, φ indicates the phase difference between V0 and V1. Thatis, by obtaining V2 among the detected voltages obtained from thepiezoelectric devices, the angular velocity in the rotating system canbe obtained.

In the case where the added masses mO in the form of individual metalmembers or the like are provided for the vibrators, it is preferablethat the weight of the added mass for each vibrator, to which the addedmass is secured, be about 10% to about 30% of the vibrator.

If the cut portions 20b are formed at the ends of the vibrator as shownin FIG. 8, it is preferable that the mass to be removed by the cutportions be about 10% to about 30% of the vibrator.

Any of the foregoing embodiments may employ the structure for providingthe added mass, in which the individual metal member is secured to thevibrator, or the structure, in which the cut portions are formed. In thecase where the flat vibrator is employed, the added mass may be formedby bending the leading portion. If the vibrator is in a columnar shape,the added mass may be formed to project over the upper surface or thelower surface of the vibrator by cutting or by molding in place offorming the cut portions.

Each vibrator according to the embodiments may be made of apiezoelectric material. In the foregoing case, a driving electrode and adetection electrode may arbitrarily be formed on the surface of each ofthe vibrators.

Fourth Embodiment

FIG. 13 shows a fourth embodiment of the present invention. FIG. 14 is aview of explanatory showing the vibration mode of the vibratorygyroscope shown in FIG. 13. FIG. 15 shows the direction of the electricfield of the crystal forming the vibrator and the crystal, the crystalorientation of which is realized by a Z-crystal plate at the cut anglerotated +2° about the X-axis, and the configuration of electrodes, FIG.15 being an enlarged cross sectional view taken along line XV--XV ofFIG. 13.

The vibratory gyroscope shown in FIG. 13 comprises a flat vibrator 41supported by a support member 42 by a cantilever method such that oneend of the vibrator 41 is rigidly held by the support member 42. As analternative to being formed from a flat material, the vibrator 41 may bein a columnar shape. In place of the cantilever method, the supportstructure may supported be such that the central portion of the vibrator41 is simply supported.

The vibrator 41 is made of a piezoelectric material In this embodimentsthe piezoelectric material is crystal (a single crystal material), thecrystal orientation of which is realized by a Z-crystal plate at a cutangle rotated +2° about the X-axis. The direction of the electric fieldof the foregoing crystal is as shown in FIG. 15. Alternatively, thevibrator 41 may be made of piezoelectric ceramic. On the upper and lowersides of the vibrator 41 (opposing the Z direction), there are disposedground electrodes 43 by bonding or stacking. Each of the groundelectrodes 43 is connected to a ground potential.

On one of the two side surfaces (opposing the X direction) there isformed a driving electrode 44. On the other side surface, a detectionelectrode 45 is formed. Each of the electrodes 43, 44 and 45 has anelongated shape extending in the direction of the major axis of thevibrator 41. Although the electrodes are omitted from illustration inFIG. 16 and ensuing figures, which are perspective views showingembodiments of the present invention, the electrodes extend in the majoraxis similarly to that shown in FIG. 13.

As shown in FIG. 15, a drive power source 46 for generating ahigh-frequency electric power is connected to the drive electrode 44.The drive electrode 44 and the drive power source 46 form a drive means.A detection lead line is connected to the detection electrode 45, and adetection output terminal 47 is formed between the foregoing lead lineand the ground potential, the detection output terminal 47 beingconnected to a detection circuit. The detection electrode 45 and thedetection output terminal 47 form the detection means according to thepresent invention. An added mass mO is provided on the leading portion(free end) of the vibrator 41. The added mass mO projects in the -Xdirection from the vibrator 41 such that the center of gravity of theadded mass mO is deviated in the -X direction with respect to thecentral axis O of the vibrator 41.

The vibratory gyroscope according to this embodiment detects the angularvelocity ω in a rotating system about the Z-axis, the detection outputcapable of detecting the rotation about the Z-axis being indicated byΩz. When high-frequency electric power is applied from the drive powersource 46 to the drive electrode 44, positive and negative distortionsare alternately generated in a portion of the crystal to which the driveelectrode 44 is connected. As a result, the vibrator 41 isbending-vibrated in the X direction (a first direction), as shown inFIG. 14. When the vibrator 41, which is being vibrated in the Xdirection, is placed in a rotating system about the Z-axis Coriolisforce in the Y direction perpendicular to the relative velocity in the Xdirection in the rotating system acts on the vibrator 41. Since theCoriolis force acts in the major axis of the vibrator 41 in theforegoing case, the added mass mO causes force +Fy in the Y direction toact on the center of gravity, which is the deviated position. The force+Fy causes moment about Z-axis acts on the leading portion of thevibrator 41. As a result, the vibrator 41 is deformation-vibrated in thefirst direction (the X direction), which is the same as the drivedirection. The deformation vibration of the vibrator 41 in the Xdirection causes the side surface of the vibrator 41 in the -X directionto be distorted. The distortion is, as the voltage (or an electriccurrent), detected by the detection electrode 45 shown in FIG. 15. Adetected voltage level (or an electric current), which is the mixture ofthe drive vibration component in the X direction and the vibrationcomponent in the X direction, can be obtained from the detection outputterminal 47. By removing the drive vibration component from the detectedvoltage, the Coriolis force in the rotating system about the Z-axis canbe detected. In accordance with the detection output of the Coriolisforce, the angular velocity ω is calculated.

When the vibratory gyroscope shown in FIG. 13 is rotated about theY-axis, Coriolis force acts in a second direction (the Z direction)perpendicular to the X direction. As a result, vibrations in the Zdirection are generated in the vibrator 41. Since the detectionelectrode 45 is disposed on the side surface (the side surface extendingin the Z direction) of the vibrator 41 that opposes the X direction, thedetection means consisting of the detection electrode 45 and thedetection output terminal 47 does not detect the vibration component inthe Z direction. As a result, only the angular velocity in the rotatingsystem about the Z-axis can be detected.

By making the vibrator 41 by polycrystal piezoelectric material and bydetermining the polarizing direction and the configuration of theelectrodes, the detection electrodes formed on the two sides opposingthe Z direction (the upper and lower surfaces shown in FIG. 15) are ableto detect vibrations in the X direction. In the foregoing case, use ofthe relationship between the dielectric polarization direction of thepiezoelectric material and the detection electrode enables a structureto be formed in which the voltage generated due to the vibrations in theZ direction is compensated between the electrodes. As a result of theforegoing structure, a structure can be formed in which the output ofthe detected rotation about the Y-axis cannot be obtained from thedetection output terminal 47. Thus, only the output denoting thedetected rotation about the Y-axis (the output denoting detected Ωy) canbe obtained.

Fifth Embodiment

FIG. 16 is a perspective view showing a vibratory gyroscope according toa fifth embodiment of the present invention. FIG. 17A is a view ofexplanatory showing a drive vibration mode, FIG. 17B is a view ofexplanatory showing a detection vibration mode, FIG. 18A is a diagramshowing the dielectric polarization direction of the piezoelectricmaterial, such as piezoelectric ceramic, and the configuration of theelectrodes, and FIG. 18B is a cross sectional view taken along lineXVIII--XVIII of FIG. 16 and showing another embodiment of the directionof the electric field of crystal and the configuration of theelectrodes.

The vibratory gyroscope according to this embodiment comprises two(plate-like) parallel vibrators 51 and 52 extending from a flat elasticmember 50. The central portion of the base of the elastic member 50 issupported by a support rod 53. The elastic member 50 and the vibrators51 and 52 are made of piezoelectric material. As shown in FIG. 16, addedmasses mO deviated in the first direction (the X direction) are disposedin the leading portions of the two vibrators 51 and 52. In each of theleading portions of the vibrators 51 and 52, the center of gravity isdeviated in the -X direction with respect to the central axis of thevibrator.

In the embodiment shown in FIG. 18A, the vibrators 51 and 52 are made ofpolycrystal material, such as piezoelectric ceramic, and the dielectricpolarization directions of which are determined as indicated by arrowsof FIG. 18A. All electrodes are formed on the two sides of the vibrators51 and 52 that oppose the Z direction. Each electrode is formed toextend in the Y direction.

The structure shown in FIG. 18A comprises drive electrodes 54 and 55 onthe two sides of the vibrator 51. Furthermore, drive electrodes 56 and57 are formed on the two sides of the vibrator 52. The foregoingelectrodes are supplied with high frequency electric power from a drivepower source 46. The drive electrodes and the drive power source 46 forma drive means. Reference numerals 58 represent ground electrodes. Thedrive power source 46 supplies electric power in the same phase to eachof the drive electrodes 54, 55, 56 and 57. When a phase at a certainmoment of the electric power supplied from the drive power source 46causes the portions of the piezoelectric material forming the driveelectrodes 54 and 56 to be negatively distorted (contraction distorted),portions of the piezoelectric material forming the drive electrodes 55and 57 are positively distorted (expansion distorted). Therefore, thevibrators 51 and 52 are vibrated in the X direction (the firstdirection) in phases which are different from each other by 180°. Thatis, when the amplitude of the vibrator 51 is in the +X direction at acertain moment as shown in FIG. 17A, the amplitude of the vibrator 52 isin the -X direction.

When the vibratory gyroscope vibrating as described above is placed in arotating system about the Z-axis, Coriolis force acts in Y directionperpendicular to the X-axis. Since the added mass mO deviated in the Xdirection is provided for each of the vibrators 51 and 52, moments aboutthe Z-axis act so that the vibrators 51 and 52 are vibrated in the firstdirection (the X direction). Since the two vibrators 51 and 52 are, asshown in FIG. 17A, being driven at a relative velocity in the oppositeamplitude directions, the Coriolis forces Fy in the Y direction areopposite to each other. Thus, when +Fy acts on either of the vibrators51 and 52, -Fy acts on the other vibrator. Therefore, the vibrators 51and 52 are vibrated in the X direction in the opposite amplitudedirections.

The vibrations in the X direction are detected by the detection means.The detection means is formed by detection means electrodes 61, 62, 63and 64. When the direction of the amplitude of the vibrations in the Xdirection generated due to the Coriolis force is as shown in FIG. 17B ata certain moment, portions of the piezoelectric material forming thedetection electrodes 61 and 63 are negatively distorted. On the otherhand, the detection electrodes 62 and 64 are positively distorted. Sincethe dielectric polarization direction in the portions in which thedetection electrodes 61 and 63 are provided, and that in the portions inwhich the detection electrodes 62 and 64 are provided, oppose eachother, detection voltages (or electric current) in the same phase can beobtained from the respective detection electrodes 61, 62, 63 and 64.Therefore, the output denoting the detected rotation about the Z-axis(the output denoting detected Ωz) can be obtained from the detectionoutput terminal 65. Note that the detection means may comprise anaddition circuit for adding the detected voltages obtained from thedetection electrodes 61, 62, 63 and 64.

If the detection output is obtained on the basis of the drive output(component), only the output due to the Coriolis force can be extracted.

When the vibratory gyroscope shown in FIG. 16 is placed in a rotatingsystem about the Y-axis, Coriolis force acts in the second direction (Zdirection) perpendicular to the first direction (X direction) which isthe drive direction. Thus, each of the vibrators 51 and 52 are vibratedin the Z direction. Since the vibrators 51 and 52 are vibrated in the Xdirection in opposite amplitudes, the directions of amplitudes of thevibrators 51 and 52 in the Z direction are in opposite phases. That is,when the direction of amplitude of the vibrator 51 is in the +Zdirection at a certain moment, the direction of amplitude of thevibrator 52 is in the -Z direction, as indicated by dashed arrows shownin FIG. 18A. When the vibrators 51 and 52 are being deformed in theforegoing directions of the amplitudes, the portion of the piezoelectricmaterial forming the detection electrode 61 is negatively distorted. Theportion of the piezoelectric material forming the detection electrode63, to which the same dielectric polarization direction is directed asthat directed to the detection electrode 61, is positively distorted.Therefore, the phases of the detection voltages (or electric currents)prom the two detection electrodes 61 and 63 are different from eachother by 180° so that the detection voltages are compensated. The samephenomenon takes place for the detection electrodes 62 and 64.

Therefore, only the vibration component in the X direction is extractedfrom the detection output terminal 65, and the vibration component inthe Z direction is not extracted. From the detection output terminal 65,only the output denoting detected Ωz, which is the output denoting thecomponent of rotation about the Z-axis, is obtained.

FIG. 18B shows a case where the vibrators 51 and 52 are made of crystal,the crystal orientation of which is realized by a Z-crystal plate at thecut angle rotated +2° about the X-axis. The arrows shown in FIGS. 18Bindicate the directions of electric fields. Each of the vibrators 51 and52 comprise a ground electrode 66. Drive electrodes 68 are formed on thetwo sides of the vibrator 51 in the Z direction, while drive electrode69 is formed on the side surface of the vibrator 52 in the -X direction.When high-frequency electric power is supplied from the drive powersource 46 to the two drive electrodes 68 and 69, the vibrators 51 and 52are vibrated in the first direction (X direction) in the phase in whichthe directions of the amplitudes oppose each other, as shown in FIGS.17A.

On the side surface of the vibrator 52 in the +X direction, there isformed a detection electrode 71. When the vibrators 51 and 52 are placedin a rotating system about the Z-axis, the Coriolis force vibrates thevibrators 51 and 52 in the X direction in the opposite amplitudedirections. Therefore, detection voltage (or an electric current) of thevibrations in the X direction can be obtained from the detectionelectrode 71. Even if vibrations in the Z direction act on the vibrators51 and 52 due to the rotations about the Y-axis, the foregoingvibrations are not detected from the detection electrode 71. Therefore,only the output denoting detected Ωz, which is the output denoting theresult of detection of rotations about the Z-axis, can be obtained.

Sixth Embodiment

FIG. 19 is a perspective view showing a vibratory gyroscope according toa third embodiment of the present invention. FIG. 20A is a view ofexplanatory showing a drive vibration mode. FIG. 20B is a view ofexplanatory showing a detection vibration mode. FIG. 21A is a diagramshowing the dielectric polarization directions of the piezoelectricmaterial forming the vibrator and the configuration of electrodes. FIG.21B is a diagram showing the directions of electric fields of crystalforming the vibrator and the configuration of electrodes of anotherembodiment FIGS. 21A and 21B are cross sectional views taken along lineXXI--XXI of FIG. 19.

The vibratory gyroscope according to this embodiment comprises three(plate-like) parallel vibrators 81, 82 and 83 extending from a flatelastic member 80. The elastic member 80 and the vibrators 81, 82 and 83are made of piezoelectric material. In the leading portions of the rightand left vibrators 81 and 82, there are disposed added masses mOdeviated in the first direction (the X direction). The directions of thedeviations of the added masses mO are opposite between the two vibrators81 and 82 such that the center of gravity is deviated in the +Xdirection with respect to the central axis of the vibrator 81 and thecenter of gravity is deviated in the -X direction with respect to thecentral axis of the vibrator 82.

In the embodiment shown in FIG. 21A the vibrators 81, 82 and 83 are madeof piezoelectric ceramic, and their dielectric polarization directionsare determined as indicated by arrows shown in FIG. 21A. Electrodes areformed on at least one of the side surfaces of each of the vibrators 81,82 and 83. All electrodes are formed to extend in the Y direction.

As shown in FIG. 21A, ground electrodes 84 are provided for thevibrators 81, 82 and 83. The drive electrodes 85, 86, 87 and 88 and thedrive power source 46 form the drive means. High-frequency electricpower Prom the drive power source 46 is, in the same phase, supplied tothe drive electrodes 85, 86, 87 and 88. The dielectric polarizationdirection of the piezoelectric material acting on the drive electrodes85 and 86 oppose the dielectric polarization direction acting on thedrive electrodes 87 and 88. Therefore, if the portions of thepiezoelectric material forming the drive electrodes 85 and 86 arenegatively distorted at a certain moment, the portions of thepiezoelectric material forming the drive electrodes 87 and 88 arepositively distorted. At the foregoing moment, the direction of theamplitudes of the right and left vibrators 81 and 82 are in the -Xdirection and the direction of the amplitude of the central vibrator 83is in the +X direction, as shown in FIG. 20A. That is, the right andleft vibrators 81 and 82 and the central vibrator 53 are driven in thesymmetrical mode to vibrate in the opposite phases in the firstdirection (the X direction).

The structure, in which the three vibrators vibrate in the symmetricalphases as described above, enables the base of the elastic member 80(having no vibrator) to be stabilized. Therefore, only a small portionof the vibrations is transmitted to the base. Therefore, even if thebase of the elastic member 80 is supported in a rigid manner as shown inFIG. 20, the vibration mode of each vibrator is not affected.

When the vibratory gyroscope, described above, is placed in a rotatingsystem about the Z-axis, Coriolis force acts in the Y direction which isperpendicular to the X-axis drive direction. Since added masses Modeviated in the X direction are provided on the right and left vibrators81 and 82, moments about the Z axis act on the vibrators 81 and 82 dueto the Coriolis force in the Y direction. As a result, the vibrators 81and 82 are vibrated in the first direction (the X direction). Since noadded mass is provided for the central vibrator 83, the Coriolis forceacts does not act on the vibrator 83, and the central vibrator 83 is notvibrated.

The right and left vibrators 81 and 82 are driven in the X direction inthe same direction of the amplitude The directions, in which the addedmasses mO are deviated in the two vibrators 81 and 82, are -X directionand +X direction (i.e., opposite to each other). When the right and leftvibrators 81 and 82 are, as shown in FIG. 20A, being driven in the -Xdirection at the relative velocity, the Coriolis forces in the Ydirection acting on the vibrators 81 and 82 in the same direction (+Fy).Therefore, the added masses mO cause the vibrators 81 and 82 to bevibrated in the X direction in the opposite amplitude directions, asshown in FIG. 20B.

In this embodiment, the vibrations of the right and left vibrators 81and 82 in the X direction are detected by the detection means. In thestructure shown in FIG. 21A, the detection means is formed by detectionelectrodes 91, 92, 93 and 94 and a detection output terminal 95. If thedirection of amplitude of the vibrations in the X direction generateddue to the Coriolis force is as shown in FIG. 20B at a certain moment,the piezoelectric material forming the detection electrodes 91 to 94 isnegatively distorted. Since the dielectric polarization directions ofthe piezoelectric material, in which the detection electrodes 91 to 94are formed, are the same, detection voltages (or electric currents) inthe same phase can be obtained from the detection electrodes 91, 92, 93and 94. Therefore, detection voltages from the detection electrodes canbe obtained through the detection output terminal as the output denotingdetected Ωz. Note that an addition circuit for adding the detectedvoltages obtained from the detection electrodes 91, 92, 93 and 94 may beprovided.

When the vibratory gyroscope is placed in a rotating system about theY-axis Coriolis force acts in the second direction (the Z direction),which is perpendicular to the first direction (the X direction), whichis the drive direction. Thus, the vibrators 81, 82 and 83 are vibratedin the Z direction by the Coriolis force. Since the right and leftvibrators 81 and 82 and the central vibrator 83 are driven to vibrate inopposite X directions, the Coriolis force in the Z direction vibratesthe right and left vibrators 81 and 82 and the central vibrator 83 inopposite directions. That is, if the directions of amplitudes of theright and left vibrators 81 and 82 are in the +Z direction at a certainmoment, the direction of the amplitude of the central vibrator 83 is inthe -Z direction, as shown in FIG. 21A.

At this time, the piezoelectric material forming the detectionelectrodes 91 and 93 is negatively distorted, while the piezoelectricmaterial forming the detection electrodes 92 and 94 is positivelydistorted. Since the dielectric polarization directions of thepiezoelectric material forming the detection electrodes 91, 92, 93 and94 are the same, detection voltages due to the vibrators in the Zdirection are compensated. Therefore, the vibration component due to theCoriolis force about the Y-axis is not detected in the detection outputterminal 95, whereas only the output denoting detected Ωz, which is theoutput denoting the result of detection of rotations about the Z-axis,is obtained.

FIG. 21B shows a case where the vibrators 81, 82 and 83 shown in FIG. 19are made of crystal, the crystal orientation of which is realized by aZ-crystal plate at the cut angle rotated +2° about the X-axis. Thearrows shown in FIG. 21B indicates the directions of electric fields. Onthe side surfaces of the right and left vibrators 81 and 83 in the -Xdirection, there are formed drive electrodes 96 and 98. On the two sidesof the central vibrator 83 in the Z direction, there is formed paireddrive electrodes 97. When high-frequency electric power is supplied fromthe drive power source 46 to the drive electrodes 96, 97 and 98, theright and left vibrators 81 and 82 and the central vibrator 83 arevibrated in the first direction (the X direction) in the phase in whichtheir amplitude directions are opposite to each other, as shown in FIG.20A.

Detection electrodes 101 and 102 are formed on the side surfaces of theright and left vibrators 81 and 82. When the vibratory gyroscope isplaced in a rotating system about the Z-axis, the right and leftvibrators 81 and 82 are, due to the Coriolis force, vibrated in the Xdirection in the opposite amplitude directions, as shown in FIG. 20B.Therefore, detection voltages in the opposite phases can be obtainedfrom the detection electrodes 101 and 1020 As a result, a differentialcircuit (a subtraction circuit) 103 is operated to obtain the differencein the detection voltage (or the electric current) between the twodetection electrodes 101 and 102. Thus, the component generated due tothe Coriolis force in the rotating system about the Z-axis can bedetected.

In the structure shown in FIG. 21B, if the vibrators 81 and 82 arevibrated in the Z direction due to the rotations about the Y-axis, theforegoing vibrations are not detected from the detection electrodes 101and 102. Thus, noise generated due to the vibrations in the Z directionis not superimposed on the output denoting detected Qz obtained from thedetection output terminal 95.

Seventh Embodiment

FIG. 22 is a perspective view showing a vibratory gyroscope according toa seventh embodiment of the present invention. FIG. 23A is a view ofexplanatory showing a drive vibration mode, and FIG. 23B is a view ofexplanatory showing a detection vibration mode. FIG. 24A is a diagramshowing the dielectric polarization directions of the piezoelectricmaterial forming the vibrators and the configurations of the electrodes.FIG. 24B is a diagram showing the directions of electric fields ofcrystal forming the vibrators and the configuration of electrodesaccording to another embodiment of the present invention. FIGS. 24A and24B are cross sectional views taken along line XXIV--XXIV of FIG. 22.

Similarly to the vibratory gyroscope according to the embodiment shownin FIG. 19, the vibratory gyroscope according to this embodimentcomprises three (plate-like) parallel vibrators 81, 82 and 83 formedintegrally with an elastic member 80 made of piezoelectric material.Although added masses mO are provided in the leading portions of theright and left vibrators 81 and 82, the structure is different from thatof the embodiment shown in FIG. 19 in that the added masses mO projectin the Z direction. The center of gravity of the vibrator 81 is deviatedin the -Z direction with respect to the central line thereof due to theadded mass mO. The center of gravity of the vibrator 82 is deviated inthe +Z direction. This embodiment enables the angular velocity ω in therotating system about the X-axis.

In the seventh embodiment, the first direction, in which the vibrators81, 82 and 83 are vibrated, is the Z direction. In the foregoing drivemode, the vibration phases of the right and left vibrators 81 and 82 andthe central vibrator 83 in the Z direction are different from each otherby 180°, as shown in FIG. 23A. When the directions of amplitudes of theright and left vibrators 81 and 82 are in the +Z direction at a certainmoment, the direction of the amplitude of the central vibrator 83 is inthe -Z direction.

When the vibratory gyroscope, which is being driven in the foregoingmode, is placed in a rotating system about the X axis, Coriolis forcesin the Y direction act on the vibrators 81, 82 and 83. Since the centralvibrator 83 has no added mass and the Coriolis force acts in the majoraxis thereof, the vibrator 83 is not vibrated. Since the right and leftvibrators 81 and 82 are driven in the same direction, Coriolis forces inthe Y direction in the same phase act on the two vibrators 81 and 82.When the right and left vibrators 81 and 82 are, in this embodiment,driven at a velocity in the +Z direction as shown in FIG. 23A, Coriolisforces in the +Fy direction act on the vibrators 81 and 82. Since theadded masses mO projecting in the Z direction in the opposite directionsare provided for the right and left vibrators 81 and 82, Coriolis forcesin the rotating system about the Z-axis vibrate the right and leftvibrators 81 and 82 in the Z direction in the opposite phases, as shownin FIG. 23B. By detecting the vibrations of the vibrators 81 and 82 inthe Z direction (the first direction), the detection output Ωx about theX-axis can be obtained.

FIG. 24A shows an embodiment in which vibrators 81, 82 and 83 are madeof piezoelectric material, that is, piezoelectric ceramic. Thedielectric polarization directions of the piezoelectric material are asindicated by arrows. The electrodes shown in FIG. 24A are formed toextend in the direction of the Y-axis. Reference numeral 105 representsground electrodes among the foregoing electrodes.

The high-frequency electric power supplied from the drive power sourceis, in the same phase, supplied to the drive electrodes 106, 107, 108and 109. In the piezoelectric material forming the drive electrodes 106,108 and 109, the dielectric polarization directions are the same. In thepiezoelectric material forming the drive electrode 107, the dielectricpolarization direction is in the opposite direction. Therefore, theright and left vibrators 81 and 82 and the central vibrator 83 aredriven in the Z direction in the opposite phase directions, as shown inFIG. 24A.

When the vibratory gyroscope is placed in a rotating system about theX-axis, the Coriolis forces vibrate the right and left vibrators 81 and82 in the Z direction in the opposite phase, as shown in FIG. 24B. Thevibrations are detected by detection electrodes 111 and 112. Thedetection electrodes 111 and 112 are vibrated in the opposite phases inthe Z direction due to the Coriolis force. In the portions of the twodetection electrodes 111 and 112, the dielectric polarizing directionare opposite to each other. Therefore, the detection voltages (orelectric currents) in the same phase can be obtained from the twodetection electrodes 111 and 112. On the other hand, the Ωx detectionoutput of the rotational component about the X-axis can be obtained fromthe detection output terminal 114.

When the vibratory gyroscope shown in FIG. 22 is placed in a rotatingsystem about the Y-axis, each of the vibrators 81, 82 and 83 is vibratedin a second direction (X direction) perpendicular to the first direction(the Z direction) which is the drive direction. Since the right and leftvibrators 81 and 82 are driven in the Z direction in the same phase asshown in FIG. 23A, the Coriolis force given in a rotating system aboutthe Y-axis causes the right and left vibrators 81 and 82 to be vibratedin the X direction in the same phase. If the amplitude directions of theright and left vibrators 81 and 82 are in the +X direction, thepiezoelectric material of the portions, in which the detectionelectrodes 111 and 112 are disposed, is negatively distorted. Since thedielectric polarizing directions oppose each other in the portions ofthe detection electrodes 111 and 112, the vibration component in the Xdirection causes the phases of the voltages (or electric currents)detected at the detection electrodes 111 and 112 to be different fromeach other by 180°. Therefore, they are compensated and are not allowedto appear at the detection output terminal 114. Therefore, only the Ωxdetection output, which is the rotation detection output about theX-axis, is obtained at the detection output terminal 114, and theCoriolis force given in the rotating system about the Y-axis is notdetected.

FIG. 24B shows the directions of electric fields in the case where thevibrators 81, 82 and 83 are made of a crystal, the direction of crystalof which is X-crystal plate at the cut angle rotated +0° about X-axis.Ground electrodes 115 are formed on the side surfaces that oppose the Xdirection of each vibrator. The high-frequency electric power issupplied from the drive power source 46 to the drive electrodes 116, 117(two portions) and 118. As shown in FIG. 23, the right and leftvibrators 81 and 82 and the central vibrator 83 are driven in theopposite amplitude directions in the Z direction.

The right and left vibrators 81 and 82 are vibrated in the oppositephases in the Z direction due to the Coriolis force in the rotatingsystem about the X-axis. The foregoing vibrations are detected by thedetection electrodes 121 and 122. As shown in FIG. 23B, the vibrationsin the Z direction to be given to the right and left vibrators 81 and 82due to the Coriolis force in the rotating system about the X-axis are inopposite phases. Since the detection voltages in opposite phases areobtained at the detection electrodes 121 and 122, the outputs from thetwo detection electrodes 121 and 122 pass through the differentialcircuit so that only the output Ωx, denoting the detected rotation aboutX-axis, is obtained at the detection output terminal 124.

When the vibratory gyroscope shown in FIG. 22 is rotated about theY-axis, the right and left vibrators 81 and 82 are vibrated in the Xdirection in the same phase. The vibrations are not detected by thedetection electrodes 121 and 122 but only the output denoting detectedΩx is obtained from the detection output terminal 124.

Eighth Embodiment

FIG. 25 is a perspective view showing a vibratory gyroscope according toan eighth embodiment of the present invention. FIG. 26A is a view ofexplanatory showing the drive vibration mode, FIG. 26B is a view ofexplanatory showing the detection vibration mode of a rotating systemabout the Z-axis and FIG. 26C is a view of explanatory showing thedetection vibration mode of a rotating system about the Y-axis. FIG. 27Ais a diagram showing the dielectric polarization directions of thepiezoelectric material forming the vibrators and the configuration ofelectrodes. FIG. 27B is a diagram showing the directions of electricfields realized when the vibrators are made of crystal and theconfiguration of the electrodes. FIGS. 27A and 27B are cross sectionalviews taken along XXVII--XXVII of FIG. 25.

The structure of the vibratory gyroscope shown in FIG. 25 is the same asthat shown in FIG. 7. The elastic member 80 has three (plate-like)vibrators 81, 82 and 83 formed integrally. The right and left vibrators81 and 82 have, in the leading portions thereof, added masses mOextending in the X direction in the opposite directions.

As shown in FIG. 26A, the vibrators 81, 82 and 83 are vibrated in thefirst direction (the X direction). Similarly to the structure shown inFIG. 19, the right and left vibrators 81 and 82 and the central vibrator83 are driven in the X direction in the opposite amplitude directions.When the vibratory gyroscope according to this embodiment is placed in arotating system about the Z-axis, the added masses mO causes the rightand left vibrators 81 and 82 to be vibrated in the X direction in theopposite amplitude direction, as shown in FIG. 26B. When the vibratorygyroscope is placed in a rotating system about the Y-axis, the right andleft vibrators 81 and 82 and the central vibrator 83 are vibrated in theZ direction in the opposite amplitude directions, as shown in FIG. 26C.

In the eighth embodiment, the detection means shown in FIG. 27A or 27Bis able to individually detect the vibrations in the rotating systemabout the Z-axis due to the Coriolis force and those in the rotatingsystem about the Y-axis due to the Coriolis force.

FIG. 27A shows the dielectric polarization directions and theconfiguration of electrodes in the case where the vibrators 81, 82 and83 are made of piezoelectric ceramic. Ground electrodes 131 are providedfor the vibrators 81, 82 and 83. The drive means is formed by the drivepower source 46, and drive electrodes 132, 133, 134 and 135. Whenhigh-frequency electric power in the same phase is supplied to each ofthe drive electrodes 132 to 135, the vibrators 81, 82 and 83 arevibrated in the mode shown in FIG. 26A.

The vibrations generated due to the Coriolis force in the rotatingsystem about the Z-axis and shown in FIG. 26B are detected by detectionelectrodes 136, 137, 138 and 139. The results of detection aretransmitted to the Ωz detection output terminal 141. Also in thisembodiment, the detection electrodes and the detection output terminalform the detection means. The output denoting detected Ωz from thedetection means is in the same phase as that of the detection voltage(or the electric current) obtained from the detection electrodes 91, 92,93 and 94. That is, only the detection output in the rotating systemabout the Z-axis is obtained from the detection output terminal 141.

The vibrations generated due to the Coriolis force of the rotatingsystem about the Y-axis and shown in FIG. 26C are obtained from thecentral vibrator 83. The vibrator 83 is provided with detectionelectrodes 142 and 143. When the vibrator 83 is vibrated in the Zdirection, detection voltages (or electric currents) in the oppositephases are obtained from the two detection electrodes 142 and 143, asshown in FIG. 26C. A differential circuit 144 acts to obtain thedifference between the detection outputs from the two detectionelectrodes 142 and 143. As a result, vibrations in the Z direction inthe vibration mode shown in FIG. 26C, that is, the rotation componentabout the Z-axis can be detected by a Ωy detection output terminal 145.

In the structure shown in FIG. 27A, the vibration component in therotating system about the Z-axis generated due to the Coriolis force isdetected by the right and left vibrators 81 and 82. The central vibrator83 is able to detect the vibration component generated due to theCoriolis force in the rotating system about the Y-axis.

FIG. 27B shows the case where the vibrators 81, 82 and 83 are made ofcrystal, the crystal orientation of which is realized by a Z-crystalplate at the cut angle rotated +2° about the X-axis. Arrows shown inFIG. 27B show the directions of electric fields. Reference numerals 153represents ground electrodes.

When high-frequency electric power is supplied from the drive powersource 46 to the two drive electrodes 153 and the drive electrode 154,the vibrators 81, 82 and 83 are driven in the vibration mode shown inFIG. 26A. The method of driving is the same as that shown in FIG. 21B.

In the vibration mode shown in FIG. 26B, the detection voltages from thedetection electrodes 155 and 156 are supplied to the differentialcircuit 157 so that the difference is obtained, similar to theembodiment shown in FIG. 21B. Thus, the output denoting the result ofdetection of rotations about the Z-axis (output denoting detected Ωz) isobtained by a detection output terminal 159.

The vibration mode shown in FIG. 26C can be obtained in such a mannerthat the detection voltages from detection electrodes 161 and 162provided for the central vibrator 83 are supplied to a differentialcircuit 163. Since the vibrator 83 is vibrated in the Z direction, theobtained difference between the output from the detection electrode 161and that from the detection electrode 162 enables the output denotingthe result of detection of rotations about the Y-axis (output denotingdetected Ωy) to be obtained at the detection output terminal 164. Alsoin the structure shown in FIG. 27B, the Coriolis force in the rotatingsystem about the Z-axis is detected by the right and left vibrators 81and 82. The central vibrator 83 is able to detect the Coriolis force inthe rotating system about the Y-axis.

In the eighth embodiment shown in FIGS. 25 to 27, Coriolis forces andangular velocities in the rotating systems about the Z-axis and Y-axiscan be detected. Each of the Coriolis forces in the rotating systemsabout the two axes can be detected by the embodiment shown in FIG. 22.Since the vibrators are driven in the Z direction in the embodimentshown in FIG. 22, the vibrators 81 and 82 are vibrated in the Zdirection due to the Coriolis force in the rotating system about theY-axis, as shown in FIG. 23B. However, each vibrator is vibrated in theX direction due to the Coriolis force in the rotating system about theY-axis. By detecting the vibrations in the Z direction from the rightand left vibrators 81 and 82 and by extracting the vibrations in the Xdirection from the central vibrator 83, the Coriolis forces and angularvelocities in the rotating systems about the X-axis and Y-axis can bedetected individually.

Ninth Embodiment

FIG. 28 is a perspective view showing a vibratory gyroscope according toa ninth embodiment of the present invention. FIG. 29 shows the vibrationmode, in which FIG. 29A shows the drive mode, FIG. 29B shows the modefor detecting rotations about the X-axis, FIG. 29C shows the mode fordetecting rotations about the Y-axis, and FIG. 29D shows a mode fordetecting rotations about the Z-axis. FIG. 30 is a diagram showing thedielectric polarization directions of the piezoelectric material and theconfiguration of electrodes. FIG. 30A is a cross sectional view takenalong line XXXA--XXXA of FIG. 28, and FIG. 30B is a cross sectional viewtaken along line XXXB--XXXB of FIG. 28.

The vibratory gyroscope according to this embodiment is arranged to becapable of individually detecting rotations about the X-axis, the Y-axisand the Z-axis. A first pair (i) of vibrators 181 and 182 are formedintegrally with and extend in parallel from a first side of an elasticmember 180, which is made of piezoelectric material. A second pair (ii)of vibrators 183 and 184 formed integrally extend from a second side ofthe elastic member 180. The vibratory gyroscope according to thisembodiment has a structure that a central portion 180a of the elasticmember 180 is secured to a support rod or suspended by a wire or thelike.

The vibrators 181 and 182 of the first pair (i) are the same as thoseshown in FIG. 16 that have, in their leading portions, the added massesmO deviated in the first direction (the X direction) with respect to thecentral axis of the vibrators 181 and 182. In the leading portions ofthe vibrators 183 and 184 of the second pair (ii), the added masses mOare disposed to be deviated in the second direction (Z direction) fromthe central axis of the vibrators 183 and 184. Each of the vibrators isdriven to a portion in which the added mass mO is provided. Thevibrators 181 and 182 of the first pair (i) are vibrated in the firstdirection (the X direction), while the vibrators 183 and 184 of thesecond pair (ii) are vibrated in the second direction (the Z direction).This embodiment is characterized in that the vibrators of the first pair(i) and vibrators of the second pair (ii) extend in the oppositedirections and the added masses and drive directions are perpendicularto each other.

The vibration method is, as shown in FIG. 29A, arranged such that thevibrators 181 and 182 of the first pair (i) are in the symmetricalvibration mode in which their amplitude directions oppose each other inthe X direction, and the vibrators 183 and 184 of the second pair (ii)are in the symmetrical vibration mode in which their amplitude directionoppose each other in the Z direction.

When the vibratory gyroscope according to this embodiment is placed inthe rotating system about the X-axis as shown in FIG. 29B, the Coriolisforce does not act on the vibrators 181 and 182 of the first pair (i).That is, the Coriolis force does not act on the vibrators 181 and 182because the vibrators 181 and 182 have no relative velocity with respectto the direction of rotation of the rotating system. Since the vibrators183 and 184 of the second pair are driven in the opposite directions inthe Z direction, the Coriolis force in the rotating system about theX-axis acts in the Y direction. Since the vibrators 183 and 184 have theadded masses mO, moments in the direction of the Y-axis are generateddue to the Coriolis force (+Fy). Thus, the vibrators 183 and 184 arevibrated in the opposite amplitude directions in the direction of theZ-axis (the same direction as the direction of the driving force).

Since the vibrators 181 and 182 of the first pair (i) are, as shown inFIGS. 29C, vibrated in the opposite phases in the X direction in therotating system about the Y-axis Coriolis forces in the direction of theZ-axis acts on the vibrators. Thus, the vibrators 181 and 182 arevibrated in the opposite amplitude directions in the Z direction. TheCoriolis forces in the X direction act on the vibrators 183 and 184 ofthe second pair (ii), which are being vibrated in the opposite phases inthe Z direction. Thus, the vibrators 183 and 184 are vibrated in theopposite amplitude directions in the X direction.

Since the vibrators 183 and 184 of the second pair (ii) are, in therotating system about the Z-axis, vibrated in the Z-axis and they haveno relative velocity with respect to the direction of rotation of therotating system, as shown in FIG. 27D, no Coriolis force acts on thevibrators 183 and 184. Since the vibrators 181 and 182 of the first pair(i) are vibrated in the X direction, the Coriolis force acts in thedirection of the Y-axis. Since the vibrators 181 and 182 are vibrated inthe opposite amplitude directions and the added masses mO of the twovibrators 181 and 182 are disposed in the same direction, the vibrators181 and 182 are vibrated in the opposite amplitude directions in the Xdirection. By detecting the vibrations of each of the vibrators shown inFIGS. 29B, 29C and 29D, the rotations about the X-axis, the Y-axis andthe Z-axis can be detected independently. In FIGS. 30A and 30B, thedirection of the dielectric polarization of the piezoelectric materialof each vibrator is indicated by an arrow.

The vibrators 181 and 182 of the first pair (i) shown in FIG. 30A haveground electrodes 185. The drive means is formed by a drive power source46 and drive electrodes 186, 187, 188 and 189. When high-frequencyelectric power in the same phase is supplied to the drive electrodes186, 187, 188 and 189, the vibrators 181 and 182 are driven in theopposite amplitude directions in the X direction.

The vibrations of the vibrators 181 and 182 of the first pair (i) in theZ direction are detected by detection electrodes 191, 192, 193 and 194.When the amplitude direction of the vibrator 181 is in the +Z directionand the vibrator 182 is in the -Z direction as shown in FIG. 29C, theportions of the piezoelectric material, in which the detectionelectrodes 191 and 194 are disposed, are negatively distorted.Conversely, the portions of the piezoelectric material, in which thedetection electrodes 192 and 193 are disposed, are positively distorted.Since the dielectric polarization directions of the piezoelectricmaterial of the portions, in which the detection electrodes 191, 192,193 and 194 are formed, are the same, differential circuits 195 and 196are so operated that the outputs from the electrodes 191 and 194 areinput to a non-inversion portion and the outputs from the electrodes 192and 193 are input to an inversion portion so that the output denotingthe result of detection of rotations about the Y-axis (output denotingdetected Ωy) is obtained from a detection output terminal 197.

The vibrators 181 and 182 are vibrated in the X direction with respectto the rotating system about the Z-axis as shown in FIG. 29D. At thistime, the detection voltages (or electric currents) obtained by thedetection electrodes 191, 192, 193 and 194 are in the same phase. Sincethe differential circuits 195 and 196 are disposed, the detectionvoltages in the same phase are compensated. Thus, output denoting thedetected rotations about the Z-axis does not appear in the detectionoutput terminal 197. The vibrations in the X direction shown in FIG. 29Dare detected by the detection electrodes 186, 187, 188 and 189 (which aswell as serve as the foregoing drive electrodes). The foregoingdetection electrodes detect the vibrations in the opposite phases in theX direction shown in FIG. 29D as the voltages (or electric currents) inthe same phase. Thus, the output denoting the results of the detectionof the rotations about the Z-axis (output denoting the detected Ωz) canbe obtained from the detection output terminal 198. Since the vibrationsin the Z direction shown in FIG. 29C are detected as the outputs in theopposite phases by the detection electrodes 187 and 188 and thedetection electrodes 186 and 189, the outputs are compensated and theydo not appear at the detection output terminal. If the detection outputis detected on the basis of the drive output (component), only theoutput due to only the Coriolis force can be extracted.

As shown in FIG. 30B, the vibrators 183 and 184 of the second pair (ii)comprises ground electrodes 201. The high frequency electric power issupplied from the drive power source 46 to the drive electrodes 202,203, 204 and 205. The dielectric polarization taking place in theportions corresponding to the drive electrodes causes the vibrators 183and 184 to be driven in the opposite amplitude directions in the Zdirection (see FIG. 29A).

The drive electrodes 202, 203, 204 and 205 also serve as detectionelectrodes. When vibrations shown in FIG. 29B are being generated,detection voltages (or electric currents) in the same phase are obtainedfrom the detection electrodes 202, 203, 204 and 205. Thus, the outputdenoting the detected rotation (the output denoting detected Ωx) aboutthe X-axis can be obtained at a detection output terminal 206.

The vibrators 183 and 184 are vibrated in the opposite phases in the Xdirection with respect to the rotating system about the Y-axis as shownin FIG. 29C. The outputs are in the opposite phases between thedetection electrodes 202 and 205 and the detection electrodes 203 and204 so that the outputs are compensated. Therefore, the output denotingthe detected rotation about the Y-axis does not appear at the detectionoutput terminal 206. If the outputs are detected on the basis of thedrive outputs (components), only the output due to the Coriolis forcecan be extracted.

In the rotating system about the Y-axis, vibrators 183 and 184 arevibrated in the opposite phases in the X direction, as shown in FIG.29C. The foregoing vibrations are detected by the detection electrodes211, 212, 213 and 214. When the direction of the amplitudes of thevibrators 183 and 184 are made as shown in FIG. 29C, detection outputsin the same phase can be obtained at the detection electrodes 211 and214. On the other hand, detection outputs, the phase of which aredeviated from the foregoing outputs by 180°, can be obtained at thedetection electrodes 212 and 213. Therefore, the outputs from theelectrodes 211 and 214 are supplied to the inversion portions ofdifferential circuits 215 and 216, whereas the outputs from theelectrodes 212 and 213 are supplied to the non-inversion portions sothat the output denoting the detected rotations about the Y-axis (theoutput denoting the detected Ωy) can be obtained at the detection outputterminal 217. When the vibrators 183 and 184 are vibrated in the Zdirection due to the rotating system about the X-axis as shown in FIGS.29B, the outputs in the same phase obtained at the electrodes 211 and212 are compensated in the differential circuit 215, whereas the outputsin the same phase from the electrodes 213 and 214 are compensated in thedifferential circuit 216. Therefore, the component of the detectedrotation about the X-axis does not appear at the detection outputterminal 217.

Although the vibrators according to the fourth to ninth embodiments areformed by piezoelectric material, they may be formed by isoelastic metalsimilar to the first to third embodiments.

In a case where the added masses mO are provided for the vibrators insuch a manner that the individual metal members or the like are securedto the vibrators, it is preferable that each added mass be about 10% toabout 30% of the mass of the vibrator to which the added mass issecured.

As described above, according to the present invention, the added massis disposed at the position deviated from the central axis of thevibrator so that, when Coriolis force acts on the added mass, thevibrator is deformed in a direction that intersects the direction inwhich the Coriolis force acts. Therefore, the vibrator isbending-deformed or torsionally deformed by the Coriolis force acting ina direction along the axial direction of the vibrator and thebending-deformation or the torsional deformation is detected so that theangular velocity in a rotating system running parallel to the axialdirection is detected.

Therefore, when the vibrator is mounted in such a manner that its axialdirection runs parallel to the surface of the substrate, the angularvelocity in a rotating system running parallel to the surface of thesubstrate can be detected. Thus, a thin detection apparatus can beformed.

If the vibrator is in the form of a flat plate, a plurality of vibratorsseparated from each other by grooves are provided to enable thevibrators to be deformed alternately so that stable vibrations can begenerated.

As described above, according to the present invention, the added massis disposed at the position deviated from the central axis of thevibrator so that, when Coriolis force acts on the added mass, thevibrator is deformed in a direction that intersects the direction inwhich the Coriolis force acts. Thus, the rotations about an axis exceptthe direction of the major axis of the vibrator can be detected so thatthe configuration of the vibrators is designed freely. As a result, thevibratory gyroscope can be disposed on a desired plane. Since thedirection, in which the vibrator is vibrated by the added mass, and thedriving direction coincide with each other, the rotations can bedetected without an influence of the Coriolis force from a rotatingsystem about an axis in the other direction.

Since the direction in which the vibrator is vibrated by the added massand the direction in which the vibrator is vibrated by the Coriolisforce in the other rotating system are made perpendicular to each other,Coriolis forces in rotating systems about two axes can individually bedetected.

By providing two sets of the vibrators, rotations about three axes canindependently be detected.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form can be changed in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:
 1. A vibratory gyroscope comprising:an elongatedvibrator having a first end, a second end, a first center of gravity,and a central axis passing from the first end to the second end throughthe first center of gravity; drive means formed on the vibrator fordeforming said vibrator in response to a signal having a predeterminedfrequency such that a portion of the vibrator located adjacent one ofthe first and second ends vibrates in a first direction perpendicular tothe central axis; a projection disposed on the portion of the vibrator,the projection having a second center of gravity which is displaced fromthe central axis such that rotation of the vibrator about an axisextending in a second direction perpendicular to the central axis duringvibration of the vibrator in the first direction causes Coriolis forceto act on said projection in a direction parallel to said central axis,thereby causing vibration of said vibrator in the first direction or inthe second direction, and detection means formed on the vibrator fordetecting said vibration of said vibrator in the first direction or inthe second direction; wherein the first direction is perpendicular tothe second direction.
 2. A vibratory gyroscope comprising:a plate-likevibrator having first and second opposing surfaces, a fixed endconnected to a support member, a free end and a central axis extendingin a direction parallel to the first and second surfaces between thefixed end and the free end; drive means located on the first and secondsurfaces for deforming said vibrator in response to a signal having apredetermined frequency such that a portion of the vibrator adjacent thefree end vibrates in a first direction perpendicular to the centralaxis; an added mass protruding from one of the first and secondsurfaces, the added mass having a center of gravity which is displacedfrom the central axis such that rotation of the vibrator about an axisextending in a second direction during vibration of the vibrator in thefirst direction causes Coriolis force to act on the added mass in adirection parallel to said central axis, thereby creating a bendingmoment causing the vibrator to bend in the first direction or in thesecond direction, and detection means formed on the first and secondsurfaces of the vibrator for detecting said bending of said vibrator inthe first direction or in the second direction, wherein the seconddirection is perpendicular to the central axis and to the firstdirection.
 3. A vibratory gyroscope comprising:a base; a first pluralityof vibrators having fixed ends integrally connected to the base and freeends, each of the first plurality of vibrators having center of gravityand a central axis extending from the fixed end to the free end throughthe center of gravity; a second plurality of vibrators having fixed endsintegrally connected to the base and free ends, each of the secondplurality of vibrators having center of gravity and a central axisextending from the fixed end to the free end through the center ofgravity; first drive means disposed on the first plurality of vibratorsfor deforming and vibrating said first plurality of said vibrator in afirst direction perpendicular to the central axes in response to asignal having a predetermined frequency; a first plurality of addedmasses, each added mass being disposed at the free end of one of thefirst plurality of vibrators and having a center of gravity which isdisplaced from the central axis such that Coriolis force caused byrotation of the vibratory gyroscope about an axis extending in thesecond direction causes the first plurality of vibrators to vibrate inthe first direction; first detection means disposed on the firstplurality of vibrators for detecting said vibration in said firstdirection resulting from Coriolis force caused by rotation of thevibratory gyroscope about an axis extending in the second direction;second detection means for detecting a vibration component applied tosaid first plurality of vibrators in a second direction perpendicular tosaid first direction resulting from Coriolis force caused by rotation ofthe vibratory gyroscope about an axis extending parallel to the centralaxis; second drive means disposed on the second plurality of vibratorsfor deforming and vibrating said second plurality of said vibrator inthe second direction in response to a signal having a predeterminedfrequency; a second plurality of added masses, each added mass beingdisposed at the free end of one of the second plurality of vibrators andhaving a center of gravity which is displaced from the central axis suchthat Coriolis force caused by rotation of the vibratory gyroscope aboutan axis extending in the first direction causes the second plurality ofvibrators to vibrate in the second direction; and third detection meansfor detecting deformation and vibrations of said second plurality ofvibrators in said second direction resulting from Coriolis force causedby rotation of the vibratory gyroscope about an axis extending in thefirst direction.
 4. A vibratory gyroscope according to claim 3, whereinsaid vibrator includes a first vibrator integrally connected to aplate-like base, the base being located at the fixed end of thevibrator, and said vibratory gyroscope further comprises:a secondvibrator integrally connected to the base and extending parallel to thefirst vibrator, the first and second vibrators being separated by agroove, the second vibrator having a second central axis which isparallel to the central axis of the first vibrator; wherein said secondvibrator includes an added mass protruding from a surface thereof, theadded mass having a center of gravity which is displaced from the secondcentral axis.